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Rapid Antigen Assays for SARS-CoV-2

Promise and Peril
Published:March 03, 2022DOI:https://doi.org/10.1016/j.cll.2022.03.001

      Keywords

      Key points

      • Rapid antigen detection tests (RADTs) for SARS-CoV-2 are most likely to be positive when viral loads are higher.
      • The diagnostic performance characteristics of RADTs vary widely among different test brands, patient populations, and symptomatic status.
      • RADTs enable more widescale scaling-up of testing globally. However, they are not appropriate as a test to determine infectiousness.
      • In practice, the use of antigen testing to screen asymptomatic persons appears to work best when combined with other public health measures and not as a sole intervention method.

      Introduction

      The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) initially caught many countries on the backfoot. The trials and tribulations of the initial roll-out of coronavirus disease 2019 (COVID-19) testing in the United States are well documented.
      • Ranney M.L.
      • Griffeth V.
      • Jha A.K.
      Critical supply shortages - the need for ventilators and personal protective equipment during the Covid-19 Pandemic.
      Although the specifics are beyond the scope of this article, they were numerous and well-publicized: from unavailability of swabs, reagents, and pipette tips to regulatory hurdles, initial testing stumbled in the United States in the face of a global pandemic caused by a novel virus.
      Although reverse transcription–polymerase chain reaction (RT-PCR) and transcription-mediated amplification (TMA, hereafter PCR) remain the gold standard for the detection of SARS-CoV-2, at the time of writing, such testing still remains predominantly confined to diagnostic laboratories.
      • Hanson Kimberly E.
      • Caliendo Angela M.
      • Arias Cesar A.
      • et al.
      Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19.
      In contrast, rapid antigen detection tests (RADTs) lend themselves to widespread deployment because of their relatively low cost, and in many cases, the ability to be run without the use of specialized equipment.
      Scaling up COVID-19 rapid antigen tests: promises and challenges - the Lancet Infectious Diseases.
      This makes testing possible for clinics, geographic areas without proximal access to laboratories, and even in one’s own home. RADTs have the potential to relieve pressure on diagnostic laboratories, who even well into 2022, continue to face labor and supply chain constraints. They represent a chance at test scalability beyond what can reasonably be achieved by diagnostic laboratory-based testing models.
      SARS-CoV-2 viral loads are similar between asymptomatic and symptomatic cases and it was recognized relatively early in the pandemic that asymptomatic individuals are an important epidemiologic driver of spread.
      • Cevik M.
      • Tate M.
      • Lloyd O.
      • et al.
      SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.
      Infrequent recovery of SARS-CoV-2 in culture after the first week of symptoms in mild-to-moderate cases, as well as the relatively high correlation between positive antigen test results and viral culture, led to the perception that RADTs could serve a role in assessing the presence of infectious virus.
      • Prince-Guerra J.L.
      • Almendares O.
      • Nolen L.D.
      • et al.
      Evaluation of Abbott BinaxNOW rapid antigen test for SARS-CoV-2 infection at two community-based testing sites — Pima County, Arizona, November 3–17, 2020.
      ,
      • Pekosz A.
      • Parvu V.
      • Li M.
      • et al.
      Antigen-based testing but not real-time polymerase chain reaction correlates with severe acute respiratory syndrome Coronavirus 2 viral culture.
      Antigen testing has been touted as key in “returning to normal,” with the concept of knowing ones “infectiousness status” having been widely popularized. Nevertheless, this concept is not without controversy or scientific counter-argument. Here, we discuss the utility of SARS-CoV-2 antigen testing, the unique opportunities it presents, and important considerations surrounding its use.

      Background

      Before the COVID-19 pandemic, RADTs for respiratory viruses were historically associated with suboptimal test performance. This was dramatically illustrated during the emergence of novel H1N1 influenza A, where sensitivities of RADTs were found to be as low as 17.8%.
      • Ginocchio C.C.
      • Zhang F.
      • Manji R.
      • et al.
      Evaluation of multiple test methods for the detection of the novel 2009 influenza A (H1N1) during the New York City outbreak.
      Meta-analyses evaluating the performance of influenza RADTs showed pooled sensitivities of 64.6% (95% confidence interval [CI], 59.0%–70.1%) and 52.2% (95% CI, 45.0%–59.3%) for influenza A and B, respectively, with pooled specificities of 98.2% (95% CI, 97.5%–98.7%). Subsequent refinements such as the use of digital readers led to tests with improved sensitivities of up to 80%,
      • Merckx J.
      • Wali R.
      • Schiller I.
      • et al.
      Diagnostic accuracy of novel and traditional rapid tests for influenza infection compared with reverse transcriptase polymerase chain reaction.
      nevertheless, RADTs for influenza are less sensitive than molecular methods, with the Centers for Disease Control and Prevention (CDC) recommending confirmatory testing of negative specimens when influenza infection is suspected.
      • Pinsky B.A.
      • Hayden R.T.
      Cost-effective respiratory virus testing.
      ,
      Important differences between SARS-CoV-2 and other respiratory viruses inform how we might think about the potential utility of antigen testing for COVID-19. Although asymptomatic transmission was initially thought to be responsible for more than half of all COVID-19 cases, more recent estimates range between 17% and 30%.
      Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: a living systematic review and meta-analysis.
      In contrast, rates of asymptomatic influenza transmission are much lower.
      • Lau L.L.H.
      • Cowling B.J.
      • Fang V.J.
      • et al.
      Viral shedding and clinical illness in naturally acquired influenza virus infections.
      Interestingly, influenza viral loads are 1 to 2 log10 copies lower among asymptomatic individuals, which may account in part for these lower transmission rates, though other studies refute this.
      • Ip D.K.M.
      • Lau L.L.H.
      • Leung N.H.L.
      • et al.
      Viral shedding and transmission potential of asymptomatic and paucisymptomatic influenza virus infections in the community.
      ,
      • Suess T.
      • Remschmidt C.
      • Schink S.B.
      • et al.
      Comparison of shedding characteristics of seasonal influenza virus (Sub)Types and influenza A(H1N1)pdm09; Germany, 2007–2011.
      To prevent transmission of SARS-CoV-2 in hospital settings, many facilities in the United States perform PCR before surgery or other procedures (eg, colonoscopy), and even upon hospital admission.
      • AF
      • BaligaChris
      • AklPascale
      • et al.
      Pre-procedural Covid-19 screening of asymptomatic patients: a model for protecting patients, community and staff during expansion of surgical care. NEJM catalyst innovations in care delivery.
      ,
      • Krüger S.
      • Leskien M.
      • Schuller P.
      • et al.
      Performance and feasibility of universal PCR admission screening for SARS-CoV-2 in a German tertiary care hospital.
      Such testing has thus further compounded test demand for SARS-CoV-2 in traditional diagnostic laboratory settings. Arguably never before in the history of laboratory medicine has there been such high diagnostic testing demand for one agent of infection. It is into this landscape that massive interest in antigen testing for COVID-19 has emerged.

      “Can I have ‘What is the reference method?’ for $800”?

      PCR is widely recognized as the most sensitive method to diagnose respiratory viral infections, having almost entirely replaced other previously commonly used test methods (ie, viral culture, direct fluorescence, etc). Nevertheless, an unfortunate and erroneous perception has emerged among the general public that PCR lacks specificity for SARS-CoV-2 detection. This stems from observations of SARS-CoV-2 RNA detectability for extended periods, long after resolution of infection.
      • Cevik M.
      • Tate M.
      • Lloyd O.
      • et al.
      SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.
      Cycle threshold (Ct) values are typically high (>35) in such cases (ie, generally above the assay’s limit of detection [LoD]) and repeat testing in these cases, therefore, oscillates between detection and nondetection.
      • He X.
      • Lau E.H.Y.
      • Wu P.
      • et al.
      Temporal dynamics in viral shedding and transmissibility of COVID-19.
      High Ct values themselves do not necessarily indicate resolved infection, as such values can also be observed early in the infection course (before an exponential increase in viral loads) as well as among patients admitted to hospital with symptomatic disease.
      • Khoshchehreh M.
      • Wald-Dickler N.
      • Holtom P.
      • et al.
      A needle in the haystack? Assessing the significance of envelope (E) gene-negative, nucleocapsid (N2) gene-positive SARS-CoV-2 detection by the Cepheid Xpert Xpress SARS-COV-2 assay.
      Importantly, analytical false-positive SARS-CoV-2 PCR results have been shown to occur extremely rarely, though issues with specific assays have been observed.
      • Chandler C.M.
      • Bourassa L.
      • Mathias P.C.
      • et al.
      Estimating the false-positive rate of highly automated SARS-CoV-2 nucleic acid amplification testing.
      • Lin L.
      • Carlquist J.
      • Sinclair W.
      • et al.
      Experience with false-positive test results on the TaqPath real-time reverse transcription-polymerase chain reaction Coronavirus Disease 2019 (COVID-19) testing platform.
      Health C for D and R
      Potential for false positive results with Abbott Molecular Inc. Alinity m SARS-CoV-2 AMP and Alinity m Resp-4-Plex AMP kits - Letter to clinical laboratory staff and health care Providers. FDA.
      RADTs detect viral protein, usually viral nucleocapsid in the case of SARS-CoV-2. Nasal and nasopharyngeal specimens are predominantly used, with throat and saliva performing poorly for several RADT brands.
      • Stokes W.
      • Berenger B.M.
      • Portnoy D.
      • et al.
      Clinical performance of the Abbott Panbio with nasopharyngeal, throat, and saliva swabs among symptomatic individuals with COVID-19.
      • Uwamino Y.
      • Nagata M.
      • Aoki W.
      • et al.
      Accuracy of rapid antigen detection test for nasopharyngeal swab specimens and saliva samples in comparison with RT-PCR and viral culture for SARS-CoV-2 detection.
      • Manabe Y.C.
      • Reuland C.
      • Yu T.
      • et al.
      Self-collected oral fluid saliva is insensitive compared with nasal-oropharyngeal swabs in the detection of severe acute respiratory syndrome Coronavirus 2 in outpatients.
      Chemiluminescent antigen tests may be compatible across all sample types.
      • Yokota I.
      • Shane P.Y.
      • Okada K.
      • et al.
      A novel strategy for SARS-CoV-2 mass screening with quantitative antigen testing of saliva: a diagnostic accuracy study.
      Although commonly referred to in the popular press as if they are monolithic, there are countless different antigen test brands available worldwide, with 45 having received emergency use authorization (EUA) by the US Food and Drug Administration (FDA) at the time of writing. Critically, not all brands perform equivalently: of 64 different antigen tests directly compared in one seminal study, only 29% met minimum performance standards defined as ≥97% sensitivity and an LoD of 60% at 100 plaque-forming units per milliliter.
      • Peto T.
      • Affron D.
      • Afrough B.
      • et al.
      COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
      ,
      Regardless of the brand tested, some common principles have emerged: (1) SARS-CoV-2 RADTs are more likely to be positive when viral loads are higher, and (2) they are less likely to be positive after the first week of symptoms. High rates of antigen positivity are generally observed when Ct values are lower (ie, higher quantities of viral RNA detected), and when it is still possible to isolate infectious (ie, replication-competent) viruses in vitro.
      • Perchetti G.A.
      • Huang M.L.
      • Mills M.G.
      • et al.
      Analytical sensitivity of the Abbott BinaxNOW COVID-19 Ag card.
      For example, although sensitivity of the Innova assay was 78.2% overall in one study, sensitivity was 97% for specimens with Ct values < 25, and 95.5% for Ct values less than 28.
      • Pickering S.
      • Batra R.
      • Merrick B.
      • et al.
      Comparative performance of SARS-CoV-2 lateral flow antigen tests and association with detection of infectious virus in clinical specimens: a single-centre laboratory evaluation study.
      Similar findings have been observed for many assays across a multitude of studies.
      • Peto T.
      • Affron D.
      • Afrough B.
      • et al.
      COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
      ,
      • Holzner C.
      • Pabst D.
      • Anastasiou O.E.
      • et al.
      SARS-CoV-2 rapid antigen test: fast-safe or dangerous? An analysis in the emergency department of an university hospital.
      It is important to recognize that Ct values vary widely and differ enormously between assays and laboratories.
      • Rhoads D.D.
      • Pinsky B.A.
      The truth about SARS-CoV-2 cycle threshold values is rarely pure and never simple.
      Furthermore, Ct values are dramatically impacted by specimen quality and can be artificially high for poor-quality specimens, with poor specimen collection contributing to falsely negative results.
      • Richard-Greenblatt M.
      • Ziegler M.J.
      • Bromberg V.
      • et al.
      Quantifying the impact of nasopharyngeal specimen quality on severe acute respiratory syndrome coronavirus 2 test performance.
      Detection of culturable virus peaks near the time of symptom onset, with the probability of isolating infectious virus reduced to 6% after 10 days of symptoms among patients with mild-moderate infection.
      • Singanayagam A.
      • Patel M.
      • Charlett A.
      • et al.
      Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19, England, January to May 2020.
      Low rates of viral culture positivity have generally been observed for upper respiratory tract specimens with high Ct values,
      • Singanayagam A.
      • Patel M.
      • Charlett A.
      • et al.
      Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19, England, January to May 2020.
      but isolation of infectious virus has been observed for extended periods among patients with severe-to-critical illness
      • Walsh K.A.
      • Spillane S.
      • Comber L.
      • et al.
      The duration of infectiousness of individuals infected with SARS-CoV-2.
      and among adults and children with prolonged severe immune compromise.
      • Folgueira M.D.
      • Luczkowiak J.
      • Lasala F.
      • et al.
      Prolonged SARS-CoV-2 cell culture replication in respiratory samples from patients with severe COVID-19.
      ,
      • Aydillo T.
      • Gonzalez-Reiche A.S.
      • Aslam S.
      • et al.
      Shedding of viable SARS-CoV-2 after immunosuppressive therapy for cancer.
      Although viral culturability is related to Ct value, cytopathic effects were observed among 43% of patients with severe infection and Ct values ≥ 26, compared with 22% for mild-to-moderate cases and even from specimens with Ct values ≥ 35 (5% in mild cases, 15% in severe cases).
      • Truong T.T.
      • Ryutov A.
      • Pandey U.
      • et al.
      Increased viral variants in children and young adults with impaired humoral immunity and persistent SARS-CoV-2 infection: a consecutive case series.
      Consequently, the relationship between high Ct values and the absence of culturability is not absolute; viral culturability can and does occur among specimens with high Ct values, albeit less frequently.
      The high correlation between culture and antigen positivity has led to the concept of RADTs as an “infectiousness test.” It has been proposed that viral culture may therefore be a more appropriate reference standard than PCR for asymptomatic testing. Nevertheless, this assumption is problematic as viral culture studies for SARS-CoV-2 published to date lack standardization.
      • Jefferson T.
      • Spencer E.A.
      • Brassey J.
      • et al.
      Viral cultures for COVID-19 infectious potential assessment - a systematic review.
      Preculture specimen handling (eg, storage at 4°C), as well as the cell line and culture protocol used, greatly impact the performance of culture.
      • Wurtz N.
      • Penant G.
      • Jardot P.
      • et al.
      Culture of SARS-CoV-2 in a panel of laboratory cell lines, permissivity, and differences in growth profile.
      Thus, although culture positivity indicates the presence of infectious virus, the absence of culture positivity itself does not definitively rule out the presence of infectious virus.

      Diagnostic performance in symptomatic populations

      Performance characteristics of RADTs compared with PCR vary in published studies, likely due to differences in study design, PCR assay used, participant recruitment and demographics, and symptom duration. Although some RADT brands show solid performance characteristics, meta-analyses show a wide range of sensitivities among symptomatic patients (68.9% average sensitivity; 95% CI, 61.8%–75.1%).
      • Dinnes J.
      • Deeks J.J.
      • Berhane S.
      • et al.
      Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection.
      Antigen testing specificity is generally high (99.6%; 95% CI, 99.0%–99.8%), though clusters of false-positive results have been described.
      A tale of two tests: vermont town left puzzled by positive, then negative, COVID-19 results - the Boston Globe.
      A summary of test performance among common brands is shown in Table 1.
      Table 1Currently available FDA-cleared SARS-CoV-2 antigen tests
      ManufacturerTest NameTechnology UsedHome-Use Option
      Over-the-counter or prescription required.
      Indicated for Asymptomatic TestingSeparate Instrument RequiredPerformance Data for Detection of SARS-CoV-2
      Abbott Diagnostics Scarborough, IncBinaxNOW COVID-19 Ag CardLateral flow immunoassayNoNoNoPPA: 84.6% (76.8%–90.6%)

      NPA: 98.5% (96.6%–99.5%)
      Abbott Diagnostics Scarborough, IncBinaxNOW COVID-19 Ag Card Home TestLateral flow immunoassayYesNoSmartphonePPA: 91.7% (73.0%–98.9%)

      NPA: 100.0% (87.7%–100.0%)
      Abbott Diagnostics Scarborough, IncBinaxNOW COVID-19 Antigen Self TestLateral flow immunoassayYesYesNoPPA: 91.7% (73.0%–98.9%)

      NPA: 100.0% (87.7%–100.0%)
      Abbott Diagnostics Scarborough, IncBinaxNOW COVID-19 Ag Card 2 Home TestLateral flow immunoassayYesYesSmartphonePPA: 91.7% (73.0%–98.9%)

      NPA: 100.0% (87.7%–100.0%)
      Abbott Diagnostics Scarborough, IncBinaxNOW COVID-19 Ag 2 CardLateral flow immunoassayNoYesNoPPA: 84.6% (76.8%–90.6%)

      NPA: 98.5% (96.6%–99.5%)
      Access Bio, Inc.CareStart COVID-19 Antigen testLateral flow immunoassayNoYesNoPPA: 93.75% (79.85%–98.27%)

      NPA: 99.32% (96.27%–99.88%)
      ACON Laboratories, Inc.Flowflex COVID-19 Antigen Home TestLateral flow immunoassayYesYesNoPPA: 93% (81%–99%)

      NPA: 100% (97%–100%)
      Becton, Dickinson and Company (BD)BD Veritor System for Rapid Detection of SARS-CoV-2Lateral flow immunoassayNoYesNoPPA: 84% (67%–93%)

      NPA: 100% (98%–100%)
      Becton, Dickinson and Company (BD)BD Veritor System for Rapid Detection of SARS-CoV-2 & Flu A + BLateral flow immunoassayNoNoNoPPA: 86.7% (75.8%–93.1%)

      NPA: 99.5% (97.4%–99.9%)
      Celltrion USA, Inc.Celltrion DiaTrust COVID-19 Ag Rapid TestLateral flow immunoassayNoYesNoPPA: 93.3% (78.7%–98.2%)

      NPA: 99.0% (94.7%–99.8%)
      Celltrion USA, Inc.Sampinute COVID-19 Antigen MIAMagnetic force-assisted electrochemical sandwich immunoassayNoNoYesPPA: 94.4% (80.0%–99.0%)

      NPA: 100.0% (88.0%–100.0%)
      DiaSorin, Inc.LIAISON SARS-CoV-2 AgChemiluminescent immunoassayNoNoNoPPA: 97.0% (84.7%–99.5%)

      NPA: 100% (96.6%–100%)
      Ellume LimitedEllume COVID-19 Home TestLateral flow immunoassayYesYesNoPPA: 95% (82%–99%)

      NPA: 97% (93%–99%)
      iHealth Labs, Inc.iHealth COVID-19 Antigen Rapid Test ProLateral flow immunoassayNoNoNoPPA: 88.2% (73.4%–95.3%)

      NPA: 100% (88.6%–100%)
      iHealth Labs, Inc.iHealth COVID-19 Antigen Rapid TestLateral flow immunoassayYesYesNoPPA: 94.3% (81.4%–98.4%)

      NPA: 98.1% (93.3%–99.5%)
      InBios International, Inc.SCoV-2 Ag Detect Rapid TestLateral flow immunoassayNoYesNoPPA: 86.67% (73.82%–93.74%)

      NPA: 100% (98.53%–100.00%)
      Luminostics, Inc.Clip COVID Rapid Antigen TestLateral flow immunoluminescent assayNoNoYesPPA: 96.96% (83.8%–99.9%)

      NPA: 100% (97.3%–100%)
      LumiraDx UK Ltd.LumiraDx SARS-CoV-2 Ag TestMicrofluidic immunofluorescence assayNoNoYesPPA: 97.6% (91.6%–99.3%)

      NPA: 96.6% (92.7%–98.4%)
      OraSure Technologies, Inc.IntelliSwab COVID-19 Rapid Test RxLateral flow immunoassayYesNoNoPPA: 84% (71%–92%)

      NPA: 98% (93%–99%)
      OraSure Technologies, Inc.IntelliSwab COVID-19 Rapid TestLateral flow immunoassayYesYesNoPPA: 84% (71%–92%)

      NPA: 98% (93%–99%)
      OraSure Technologies, Inc.IntelliSwab COVID-19 Rapid Test ProLateral flow immunoassayNoYesNoPPA: 84% (71%–92%)

      NPA: 98% (93%–99%)
      Ortho Clinical Diagnostics, Inc.VITROS Immunodiagnostic Products SARS-CoV-2 Antigen Reagent PackChemiluminescent immunoassayNoNoYesPPA: 80.0% (56.6%–88.5%)

      NPA: 100.0% (95.2%–100.0%)
      Princeton BioMeditech CorpStatus COVID-19/FluLateral flow immunoassayNoNoNoPPA: 93.9% (83.5%–97.9%)

      NPA: 100% (95.2%–100%)
      Qorvo Biotechnologies, LLCOmnia SARS-CoV-2 Antigen TestBulk acoustic wave biosensorNoNoYesPPA: 89.47% (78.88%–95.09%)

      NPA: 100% (89.28%–100%)
      Quanterix CorporationSimoa SARS-CoV-2 N Protein Antigen TestParamagnetic microbead-based immunoassayNoNoYesPPA: 97.7% (92.03%–99.72%)

      NPA: 100% (90.75%–100.0%)
      Quidel CorporationSofia SARS Antigen FIALateral flow immunofluorescence assayNoYesYesPPA: 96.7% (83.3%–99.4%)

      NPA: 100% (97.9%–100.0%)
      Quidel CorporationSofia 2 Flu + SARS Antigen FIALateral flow immunofluorescence assayNoNoYesPPA: 95.2% (84.2%–98.7%)

      NPA: 100.0% (96.9%–100.0%)
      Quidel CorporationQuickVue SARS Antigen TestLateral flow immunoassayNoNoNoPPA: 96.6% (88.3%–99.0%)

      NPA: 99.3 (96.0%–99.9%)
      Quidel CorporationQuickVue At-Home COVID-19 TestLateral flow immunoassayYesNoNoPPA: 84.8% (71.8%–92.4%)

      NPA: 99.1% (95.2%–99.8%)
      Quidel CorporationQuickVue At-Home OTC COVID-19 TestLateral flow immunoassayYesYesNoPPA: 83.5% (74.9%–89.6%)

      NPA: 99.2% (97.2%–99.8%)
      Salofa OySienna-Clarity COVID-19 Antigen Rapid Test CassetteLateral flow immunoassayYesNoNoPPA: 87.5% (68.6%–93.0%)

      NPA: 98.9% (94.2%–99.9%)
      a Over-the-counter or prescription required.
      Interpretation of studies regarding the performance of antigen testing among symptomatic patients can be challenging, even for assays considered to be among the most sensitive on the market. For example, among symptomatic participants at a community testing site in Wisconsin, the sensitivity of the Abbott BinaxNOW Ag Card (BinaxNOW) lateral flow immunoassay was 78.6% (95% CI, 73.4%–83.3%) compared with RT-PCR,
      • Shah M.M.
      • Salvatore P.P.
      • Ford L.
      • et al.
      Performance of repeat BinaxNOW SARS-CoV-2 antigen testing in a community setting, Wisconsin, november-december 2020.
      but was 95.4% (95% CI, 90.2%–98.3%) among symptomatic participants at a community testing site based in San Francisco
      • Pilarowski G.
      • Marquez C.
      • Rubio L.
      • et al.
      Field performance and public health response using the BinaxNOW TM Rapid SARS-CoV-2 antigen detection assay during community-based testing.
      and 94.1% (95% CI, 71.1%–100%) at a similar site in the Netherlands.
      • Van der Moeren N.
      • Zwart V.F.
      • Lodder E.B.
      • et al.
      Evaluation of the test accuracy of a SARS-CoV-2 rapid antigen test in symptomatic community dwelling individuals in The Netherlands.
      Although some studies show high sensitivity for antigen testing in hospital settings, other studies have reported sensitivities as low as 66.4% (95% CI, 57.0%–74.9%).
      • Kilic A.
      • Hiestand B.
      • Palavecino E.
      Evaluation of performance of the BD Veritor SARS-CoV-2 chromatographic immunoassay test in patients with symptoms of COVID-19.
      For assays that use digital readers, the Quidel SOFIA SARS Antigen Fluorescent Immunoassay (FIA) had 80.0% sensitivity (95% CI, 64.4%–90.9%) and 98.9% specificity (95% CI, 96.2%–99.9%) among symptomatic participants at 2 university campuses in Wisconsin, lower than what was reported in the FDA EUA.
      • Pray I.W.
      • Ford L.
      • Cole D.
      • et al.
      Performance of an antigen-based test for asymptomatic and symptomatic SARS-CoV-2 testing at two university campuses - Wisconsin, september-october 2020.
      A different study observed an 82% positive agreement with RT-PCR among symptomatic patients at an urgent care center.
      • Peto T.
      • Affron D.
      • Afrough B.
      • et al.
      COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
      The FIA also had comparable performance to the BD Veritor (Veritor) chromatographic digital immunoassay antigen test in specimens collected from drive-through and outpatient sites, despite apparent differences in sensitivity according to their respective EUA submission data.
      • Young S.
      • Taylor S.N.
      • Cammarata C.L.
      • et al.
      Clinical evaluation of BD Veritor SARS-CoV-2 point-of-care test performance compared to PCR-based testing and versus the sofia 2 SARS antigen point-of-care test.
      It is generally accepted that RADTs are unlikely to be positive beyond 7 days of symptoms, though this can differ somewhat by RADT brand (ie, 5 days vs 7 days). For example, the Innova assay remained positive for several days longer than the SureScreen F assay in one study.
      • Pickering S.
      • Batra R.
      • Merrick B.
      • et al.
      Comparative performance of SARS-CoV-2 lateral flow antigen tests and association with detection of infectious virus in clinical specimens: a single-centre laboratory evaluation study.
      Test performance may also be influenced by the number of symptoms present. For instance, the Veritor assay had 66.7% (95% CI, 30.0%–90.3%) positive agreement with PCR for patients with one symptom within 5 days of onset, compared with 88.0% (95% CI, 70.0%–95.8%) agreement among patients with at least 2 symptoms.
      • Young S.
      • Taylor S.N.
      • Cammarata C.L.
      • et al.
      Clinical evaluation of BD Veritor SARS-CoV-2 point-of-care test performance compared to PCR-based testing and versus the sofia 2 SARS antigen point-of-care test.
      RADT performance among pediatric patients has been variable between studies. Slightly lower concordance with RT-PCR was observed among children compared with adults (82% vs 85%, respectively).
      • Ford L.
      • Whaley M.J.
      • Shah M.M.
      • et al.
      Antigen test performance among children and adults at a SARS-CoV-2 community testing site.
      Among symptomatic hospitalized kids, one study reported greater than 95% sensitivity for the PanBio assay,
      • Eleftheriou I.
      • Dasoula F.
      • Dimopoulou D.
      • et al.
      Real-life evaluation of a COVID-19 rapid antigen detection test in hospitalized children.
      but a much lower sensitivity of 45.4% (95% CI, 34.1%–57.2%) was observed in a different large multihospital study.
      • Villaverde S.
      • Domínguez-Rodríguez S.
      • Sabrido G.
      • et al.
      Diagnostic accuracy of the panbio severe acute respiratory syndrome coronavirus 2 antigen rapid test compared with reverse-transcriptase polymerase chain reaction testing of nasopharyngeal samples in the pediatric population.
      These divergent results may reflect differences in performance in adults versus children, regional differences in patient population, or differences in PCR methodology.
      Symptomatic testing is arguably the most high-stakes application for RADTs. Antigen testing has limited utility in the diagnosis of symptomatic COVID-19 in hospital settings because patients who require hospitalization can present for evaluation after more than 1 week of symptoms. For this reason, they have been deemed to be unsuitable for rapid “rule-out” in an emergency department setting.
      • Holzner C.
      • Pabst D.
      • Anastasiou O.E.
      • et al.
      SARS-CoV-2 rapid antigen test: fast-safe or dangerous? An analysis in the emergency department of an university hospital.
      ,
      • Osterman A.
      • Baldauf H.M.
      • Eletreby M.
      • et al.
      Evaluation of two rapid antigen tests to detect SARS-CoV-2 in a hospital setting.
      In nonhospital settings, however, the results of laboratory-based testing can take several days to return when demand is high, which makes it impractical for symptomatic people to isolate pending their test results. Thus, the primary benefit of a positive RADT result in symptomatic individuals in the community is the ability to facilitate immediate self-isolation when positive. However, low viral loads (and thus RADT-negativity) can occur during infection due to the natural course of illness, as well as due to suboptimal sample collection. Care must be taken to interpret tests in the context of symptoms and exposures, which both influence pretest probabilities. Finally, with the increasing prevalence of disease, it is important to remember that the negative predictive value of RADTs decreases.
      Scaling up COVID-19 rapid antigen tests: promises and challenges - the Lancet Infectious Diseases.
      Thus, the CDC currently recommends negative antigen results in the presence of symptoms should be confirmed with a molecular-based test.
      CDC. Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens for COVID-19. Centers for Disease Control and Prevention.

      Performance as a test of infectiousness in asymptomatic populations

      The ability of antigen testing to identify infectious asymptomatic or presymptomatic individuals, facilitating prompt self-isolation and breakage of transmission chains is an important application of this technology. RADT positivity drops steeply after infectious virus is no longer detected by cell culture, with a sensitivity of 23.8% at the end of 1 week of initial culture positivity compared with 85.7% for PCR in one study.
      • Walsh K.A.
      • Spillane S.
      • Comber L.
      • et al.
      The duration of infectiousness of individuals infected with SARS-CoV-2.
      Antigen testing has therefore been suggested as a proxy for infectiousness; however, there is currently no infectiousness test for COVID-19 and the infectious dose of SARS-CoV-2 remains unknown. Detection of subgenomic (sg) RNA or minus-strand RNA indicates the presence of active viral replication and is generally interpreted as signifying that infectious virus may be present.
      • Hogan C.A.
      • Huang C.
      • Sahoo M.K.
      • et al.
      Strand-specific reverse transcription PCR for detection of replicating SARS-CoV-2.
      However, the relationship between sgRNA and culture positivity itself is somewhat controversial.
      • Binnicker M.J.
      Can testing predict SARS-CoV-2 infectivity? The potential for certain methods to be a surrogate for replication-competent virus.
      For better or worse, viral culture has become the de facto method for assessing infectiousness for COVID-19, with the limitations of viral culture having been discussed earlier.
      • Brümmer L.E.
      • Katzenschlager S.
      • Gaeddert M.
      • et al.
      Accuracy of novel antigen rapid diagnostics for SARS-CoV-2: a living systematic review and meta-analysis.
      A major assumption has been that false-negative RADT results represent previously infected individuals with prolonged low-level detection by PCR. However, positivity by PCR generally can also precede RADT positivity by approximately 1 to 2 days,
      • Pickering S.
      • Batra R.
      • Merrick B.
      • et al.
      Comparative performance of SARS-CoV-2 lateral flow antigen tests and association with detection of infectious virus in clinical specimens: a single-centre laboratory evaluation study.
      and 75% of false-negative RADT results in one community study occurred among individuals who were presymptomatic.
      • Ford L.
      • Whaley M.J.
      • Shah M.M.
      • et al.
      Antigen test performance among children and adults at a SARS-CoV-2 community testing site.
      In the same study, 11.8% of false-negative RADT specimens were culture positive with 53% being sgRNA positive. Thus, the proportion of false-negative RADT results that represent previous infection, rather presymptomatic infection (and thus potentially infectiousness), likely differs, depending on where in the epidemic curve a particular community is at that time because a greater proportion of people are early in the infection when cases are on the rise.
      • Hay J.A.
      • Kennedy-Shaffer L.
      • Kanjilal S.
      • et al.
      Estimating epidemiologic dynamics from cross-sectional viral load distributions.
      For antigen testing to have utility as an “infectiousness test,” one assumes that transmission is not generally readily observed among individuals with viral loads lower than what are reliably detected by RADTs. However, this does not necessarily appear to be the case. Firstly, significant overlap in Ct values occurs between spreaders and nonspreaders alike, including documented transmission by individuals with high Ct values.
      • Tian D.
      • Lin Z.
      • Kriner E.M.
      • et al.
      Ct values do not predict severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) transmissibility in college students.
      Secondly, individuals with low viral loads, defined in one study as 1×106 copies/mL, had a secondary attack rate that was half that of individuals with high viral loads, but was still significant at 12%.
      • Marks M.
      • Millat-Martinez P.
      • Ouchi D.
      • et al.
      Transmission of COVID-19 in 282 clusters in Catalonia, Spain: a cohort study.
      When the rate of local spread is high, the detection rate of RADTs for specimens with lower viral loads could potentially miss a sizable portion of presymptomatic and asymptomatic cases.
      • Wan Z.
      • Zhao Y.
      • Lu R.
      • et al.
      Rapid antigen detection alone may not be sufficient for early diagnosis and/or mass screening of COVID-19.
      Importantly, although the LoD of the BinaxNOW COVID-19 Antigen Card (Abbott, Scarborough, Maine) was shown to be approximately 4.0 × 104 to 8.1 × 104 copies per swab,
      • Perchetti G.A.
      • Huang M.L.
      • Mills M.G.
      • et al.
      Analytical sensitivity of the Abbott BinaxNOW COVID-19 Ag card.
      the LoD for several other RADT brands were shown to be much higher, at 2.1 × 106 to 2.9 × 107 per swab.
      • Corman V.M.
      • Haage V.C.
      • Bleicker T.
      • et al.
      Comparison of seven commercial SARS-CoV-2 rapid point-of-care antigen tests: a single-centre laboratory evaluation study.
      As such, transmission can and does occur among individuals with viral loads that could reasonably be expected to test negative by RADTs. Critically, transmission dynamics are influenced by several factors beyond solely viral load; these include the contact pattern (eg, duration of exposure, activity), host factors (eg, age), and the environment (eg, ventilation).
      • Cevik M.
      • Marcus J.L.
      • Buckee C.
      • et al.
      Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) transmission dynamics should inform policy.
      Thus, a negative RADT result in an asymptomatic individual should not be thought of as a definitive statement on noninfectiousness, but rather, indicating likely noninfectiousness at the time of sampling.
      Initial modeling data suggested that more frequent serial testing can mitigate concerns over RADT sensitivity
      • Larremore D.B.
      • Wilder B.
      • Lester E.
      • et al.
      Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening.
      ,
      • See I.
      • Paul P.
      • Slayton R.B.
      • et al.
      Modeling effectiveness of testing strategies to prevent Coronavirus disease 2019 (COVID-19) in nursing homes—United States, 2020.
      because the sensitivity of antigen testing before the first day of detectable shedding of infectious virus was 37.5% compared with 65% for RT-PCR. For this reason, FDA EUAs for asymptomatic testing specify that serial testing should be performed. Recently, 2 studies using real-world data have confirmed the results of initial modeling studies. In a large study among college students, weekly nasal PCR testing had a sensitivity of 98.7% for COVID-19 screening detection, with comparable sensitivities for RADTs (>98%) performed every third day, dropping to 79.7% when performed only weekly.
      • Smith R.L.
      • Gibson L.L.
      • Martinez P.P.
      • et al.
      Longitudinal assessment of diagnostic test performance over the course of acute SARS-CoV-2 Infection.
      During an intercollegiate program of daily RADT and weekly paired PCR/antigen testing (81,175 and 23,462 tests, respectively), daily antigen testing had similar sensitivities to twice-to-thrice weekly PCR testing.
      • Harmon K.
      • de St Maurice A.M.
      • Brady A.C.
      • et al.
      Surveillance testing for SARS-COV-2 infection in an asymptomatic athlete population: a prospective cohort study with 123 362 tests and 23 463 paired RT-PCR/antigen samples.
      At face value, it could be argued asymptomatic testing has few downsides because any case detected is one that would otherwise have not been detected. From this perspective, the tests are viewed as a public health intervention rather than as a diagnostic, which was their intended design.
      • Ricks S.
      • Kendall E.A.
      • Dowdy D.W.
      • et al.
      Quantifying the potential value of antigen-detection rapid diagnostic tests for COVID-19: a modelling analysis.
      ,
      • Schwartz K.L.
      • McGeer A.J.
      • Bogoch II,
      Rapid antigen screening of asymptomatic people as a public health tool to combat COVID-19.
      However, false-negative test results have clinical consequences for the individual and can also influence the behavior of the test recipient in a fashion that promotes spread of the virus to others. A negative test result (whether PCR or antigen) is not a replacement for other public health measures and the same considerations that influence test performance in symptomatic individuals (eg, specimen quality, timing of testing) are similarly a consideration in this setting.
      An additional concern is that even a test with excellent specificity will have a poor positive predictive value (PPV) during periods of low infection prevalence.
      • García-Fiñana M.
      • Buchan I.E.
      Rapid antigen testing in COVID-19 responses.
      ,
      Health C for D and R
      Potential for false positive results with antigen tests for rapid detection of SARS-CoV-2 - Letter to clinical laboratory staff and health care Providers. FDA.
      For example, PPV is predicted to be only 28.8% for a test with 98% specificity when disease prevalence is 1%.
      • Pettengill M.A.
      • McAdam A.J.
      Can we test our way out of the COVID-19 Pandemic?.
      This was also shown in a real-world study where a 66.7% false-positivity rate was noted for RADTs.
      • Pray I.W.
      • Ford L.
      • Cole D.
      • et al.
      Performance of an antigen-based test for asymptomatic and symptomatic SARS-CoV-2 testing at two university campuses - Wisconsin, september-october 2020.
      A different study performed in August 2020 reported that 23 of 39 (60%) of samples positive by RADT were negative by RT-PCR across several skilled nursing facilities.
      • Azzam Ihsan
      • Pandori Mark
      • Sherych Lisa
      Discontinue the use of antigen testing in skilled nursing facilities until further notice.
      The reasons for this cluster of false positives were never fully determined but could represent issues with poor quality test manufacturing. Concerns over test specificity can be mitigated by requiring positive results in asymptomatic people to be confirmed by secondary testing, which is recommended by the current CDC interim guidelines.
      CDC. Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens for COVID-19. Centers for Disease Control and Prevention.
      However, such confirmation may not necessarily be required when community infection rates are high. It is therefore important to continually reevaluate the prevalence of infection in a region where antigen testing will be implemented. Unfortunately, as in-home RADT becomes more available in the United States, a system for linkage to confirmatory PCR testing and to public health surveillance systems continues to be lacking, which leads to underestimates of disease prevalence.

      Asymptomatic antigen testing in practice

      Several studies modeled the potential impact of widespread antigen testing to screen asymptomatic populations, with some even factoring in behaviors such as unwillingness to test or isolate.
      • Larremore D.B.
      • Wilder B.
      • Lester E.
      • et al.
      Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening.
      ,
      • See I.
      • Paul P.
      • Slayton R.B.
      • et al.
      Modeling effectiveness of testing strategies to prevent Coronavirus disease 2019 (COVID-19) in nursing homes—United States, 2020.
      ,
      • Paltiel A.D.
      • Zheng A.
      • Sax P.E.
      Clinical and economic effects of widespread rapid testing to decrease SARS-CoV-2 Transmission.
      One study predicted that with a test sensitivity of 80%, weekly testing would prevent almost 3 million cases and over 16,000 deaths in the United States.
      • Paltiel A.D.
      • Zheng A.
      • Sax P.E.
      Clinical and economic effects of widespread rapid testing to decrease SARS-CoV-2 Transmission.
      There are 5 main areas where asymptomatic antigen testing has been applied in practice and we will review each of these applications here.

      Antigen Testing as a Circuit Breaker

      Mass population testing has been implemented by some governments in an attempt to halt exponential increases in case numbers. RADT testing with swabs collected under supervision from military personnel was used in a large-scale community testing initiative over 6 months in the city of Liverpool. This intervention led to an estimated 18% increase (95% CI, 7%–29%) in case detection, a 21% reduction (95% CI, 12%–27%) in cases during the first 6 weeks compared with control areas, but had no significant impact on the number of hospital admissions.
      University of Liverpool
      Liverpool Covid-SMART community testing Pilot evaluation Report.;.
      Notably, in interviews with participants who chose not to test, the biggest barriers to participation were fear of income loss, skepticism over the need to test, as well as crowded and inconvenient waiting lines.
      University of Liverpool
      Liverpool Covid-SMART community testing Pilot evaluation Report.;.
      Arguably, it is Slovakia’s experience that has driven the narrative about the power of mass antigen testing to halt case surges. The results from Slovakia are indeed striking: after one round of mass antigen testing, the prevalence of SARS-CoV-2 decreased by 58% (95 CI, 57%–58%). In districts that had a positivity rate ≥0.7%, a second round of testing was performed, after which a 0.3 decrease in the reproductive number (ie, R0) occurred 2 weeks later.
      • Kahanec M.
      • Lafférs L.
      • Schmidpeter B.
      The impact of repeated mass antigen testing for COVID-19 on the prevalence of the disease.
      Mass antigen testing revealed 5594 cases compared with only 782 cases that would have otherwise been identified by routine clinical testing. Disease prevalence decreased from 3.97% to 1% 1 week later with modeling data suggesting that 46,137 infections were prevented as a result of the program.
      • Frnda J.
      • Durica M.
      On Pilot massive COVID-19 testing by antigen tests in Europe. Case study: Slovakia.
      Importantly, mass antigen testing was not the sole public health intervention used by the Slovakian government; noncompliance in the testing program required a 10-day home quarantine, with random police inspections and a fine equivalent to 1.5× the national monthly wage issued for those caught breaking quarantine. Other measures implemented included limiting gatherings of more than 50 people and closure of restaurants and schools.
      • Pavelka M.
      • Van-Zandvoort K.
      • Abbott S.
      • et al.
      The impact of population-wide rapid antigen testing on SARS-CoV-2 prevalence in Slovakia.
      Though it was concluded that frequent mass testing would be necessary to sustain the decrease in cases, nevertheless, the Slovakian experience shows the potential of mass testing when combined with other measures. In practice, such measures would likely be considered unpalatable to a significant proportion of the US populace.

      Daily Testing to Enable Close Contact

      Daily antigen testing with the SOFIA assay (Quidel, San Diego, California), in addition to weekly PCR testing, was implemented by universities in the United States to facilitate the continuation of intercollegiate sports programs.
      • Harmon K.
      • de St Maurice A.M.
      • Brady A.C.
      • et al.
      Surveillance testing for SARS-COV-2 infection in an asymptomatic athlete population: a prospective cohort study with 123 362 tests and 23 463 paired RT-PCR/antigen samples.
      In all, 172 athletes had SARS-CoV-2 detected, with 52% identified as positive on days between weekly PCR tests. In all, 234 days of potential infectiousness were avoided as a result of the daily antigen testing program. There were also 98 false-positive RADT results, but negative impact was minimized by ready access to PCR results with rapid turnaround time.
      The authors observed that antigen positivity lagged about 1 day behind PCR detection. Even with nurse-supervised specimen collection, daily antigen testing failed to prevent outbreaks on 2 occasions involving a total of 32 individuals.
      • Moreno G.K.
      • Braun K.M.
      • Pray I.W.
      • et al.
      Severe Acute Respiratory Syndrome Coronavirus 2 transmission in intercollegiate athletics not fully mitigated with daily antigen testing.
      PCR results were available for the initial false-negative RADT result in 1 of the 2 index cases: despite a low Ct value of 15.9, the patient tested negative by RADT but subsequently developed symptoms later the same day. Mass PCR testing was performed 7 times during these outbreaks, leading to the identification of 21 new cases, 86% of whom were antigen negative. The most likely reason for the false-negative antigen test results in contact tracing networks is due to individuals being too early in their infection curve to be detectable by RADTs. In support of this, transmission was only interrupted when serial PCR was performed during the outbreak to identify additional cases. The study’s authors concluded that “serial antigen testing may have limited sensitivity for detecting early asymptomatic infections,
      • Moreno G.K.
      • Braun K.M.
      • Pray I.W.
      • et al.
      Severe Acute Respiratory Syndrome Coronavirus 2 transmission in intercollegiate athletics not fully mitigated with daily antigen testing.
      suggesting a two-tier strategy of antigen tests backed by intensive PCR sampling as the optimal approach for surveillance and containment.

      To Attend Events or to Travel

      The utility of day-of-testing to attend live, indoor concerts was investigated in 2 studies conducted in Catalonia, Spain. Attendees were tested using the Panbio assay (Abbott, Scarborough, Maine) before entry at a live music concert. Follow-up studies 8 days later showed no difference in COVID-19 incidence between the control and intervention groups.
      • Revollo B.
      • Blanco I.
      • Soler P.
      • et al.
      Same-day SARS-CoV-2 antigen test screening in an indoor mass-gathering live music event: a randomised controlled trial.
      Importantly, concertgoers were required to wear N95 face masks, the venue was well-ventilated, and there were restrictions on direction of movement and crowding in smaller spaces. In a follow-up study by the same group looking at a 5000-person event using the same combination of additional public health measures, 6 RADT positive and likely infectious individuals, along with 2 of their close contacts, were prevented from attending the concert.
      • Llibre J.M.
      • Videla S.
      • Clotet B.
      • et al.
      Screening for SARS-CoV-2 antigen before a live indoor music concert: an observational study.
      Only 6 cases were diagnosed within 2 weeks of the event, 3 of whom were identified as being close contacts of COVID-19 case who did not attend the concert. Although it is not possible to discern the specific impact of antigen testing per se, both studies showed that mass day-of-event RADT testing, when combined with masking and adequate ventilation, facilitates normalization of activity and mass gatherings.
      Day-of-testing was also used to screen passengers at 2 major US airports before and immediately after their flights.
      • Tande A.J.
      • Binnicker M.J.
      • Ting H.H.
      • et al.
      SARS-CoV-2 testing prior to International Airline Travel, december 2020-may 2021.
      Antigen testing detected 4 individuals (0.04%), who tested positive by both antigen testing and confirmatory RT-PCR.
      • Tande A.J.
      • Binnicker M.J.
      • Ting H.H.
      • et al.
      SARS-CoV-2 testing prior to International Airline Travel, december 2020-may 2021.
      Concerningly, as infection prevalence was estimated to be low at 1.1% at the time, there were 12 false-positive rapid antigen tests results out of 9849 total tested that did not confirm by RT-PCR.
      • Tande A.J.
      • Binnicker M.J.
      • Ting H.H.
      • et al.
      SARS-CoV-2 testing prior to International Airline Travel, december 2020-may 2021.
      This testing occurred in addition to other interventions already in place, for example, masking, vaccination, and distancing.

      Postexposure Testing in Schools

      RADTs have been tool to limit SARS-CoV-2 transmission in schools. In a randomized study involving secondary schools and colleges, students and staff with known exposure to an infected contact were either required to self-isolate for 10 days (control group) or given the option to continue attending school provided with daily RADT testing (intervention group).
      • Young B.C.
      • Eyre D.W.
      • Kendrick S.
      • et al.
      Daily testing for contacts of individuals with SARS-CoV-2 infection and attendance and SARS-CoV-2 transmission in English secondary schools and colleges: an open-label, cluster-randomised trial.
      Overall positivity postexposure was low at ∼2% in both groups, and the impact of RADT alone is difficult to assess as other safety precautions were in place, for example, masking. School absences were also not significantly reduced in the intervention group.
      • Young B.C.
      • Eyre D.W.
      • Kendrick S.
      • et al.
      Daily testing for contacts of individuals with SARS-CoV-2 infection and attendance and SARS-CoV-2 transmission in English secondary schools and colleges: an open-label, cluster-randomised trial.

      Performance of At-Home Testing

      Though some governments have provided at-home testing to their residents free-of-charge (eg, the United Kingdom and the United States), the overwhelming majority of studies to date on antigen testing involve performance by trained staff.
      • Pilarowski G.
      • Marquez C.
      • Rubio L.
      • et al.
      Field performance and public health response using the BinaxNOW TM Rapid SARS-CoV-2 antigen detection assay during community-based testing.
      ,
      • Pollock N.R.
      • Jacobs J.R.
      • Tran K.
      • et al.
      Performance and implementation evaluation of the Abbott BinaxNOW rapid antigen test in a high-throughput drive-through community testing site in Massachusetts.
      The performance of at-home RADTs is relatively understudied by comparison. Though studies show only minor differences in performance between health care worker (HCW)-collected and HCW-supervised specimen collection,
      • Klein J.A.F.
      • Krüger L.J.
      • Tobian F.
      • et al.
      Head-to-head performance comparison of self-collected nasal versus professional-collected nasopharyngeal swab for a WHO-listed SARS-CoV-2 antigen-detecting rapid diagnostic test.
      the performance of at-home, unsupervised specimen collection may differ. In a study looking at the performance of SARS-CoV-2 RT-PCR, home-collected specimens had a sensitivity of 80% compared with clinician-collected swabs
      • McCulloch D.J.
      • Kim A.E.
      • Wilcox N.C.
      • et al.
      Comparison of unsupervised home self-collected midnasal swabs with clinician-collected nasopharyngeal swabs for detection of SARS-CoV-2 Infection.
      ; such differences would also be expected to apply to RADTs. Similarly, testing performed by laboratory scientists was 78.8% sensitive compared with fully trained research HCWs (70%), with both groups exceeding the sensitivity of self-trained members of the public (57.5%).
      • Peto T.
      • Affron D.
      • Afrough B.
      • et al.
      COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
      Rates of positivity were similar between the different collectors for specimens with low Ct values, but differences became more pronounced for specimens with Ct values in the 25–28 range.
      • Peto T.
      • Affron D.
      • Afrough B.
      • et al.
      COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
      Finally, one infrequently discussed element with regards to at-home testing is the potential for test transportation/shipping conditions to deleteriously impact test performance. False-negative results were noted when test kits stored at high temperatures, with false-positive results observed with lower temperatures.
      • Haage V.
      • Ferreira de Oliveira-Filho E.
      • Moreira-Soto A.
      • et al.
      Impaired performance of SARS-CoV-2 antigen-detecting rapid diagnostic tests at elevated and low temperatures.

      Conclusions and future considerations

      Variants

      Antigen testing appears to thus far be unaffected by the emergence of SARS-CoV-2 variants at least with respect to the performance of the BinaxNOW (Abbott) assay, showing equivalent performance for major variants including the Delta variant (B.1.617)
      • Frediani J.K.
      • Levy J.M.
      • Rao A.
      • et al.
      Multidisciplinary assessment of the Abbott BinaxNOW SARS-CoV-2 point-of-care antigen test in the context of emerging viral variants and self-administration.
      and Omicron variant (B.1.429).

      Kanjilal S, Chalise S, Shah AS, et al. Analytic Sensitivity of the Abbott BinaxNOWTM Lateral Flow Immunochromatographic Assay for the SARS-CoV-2 Omicron Variant.; 2022. doi:10.1101/2022.01.10.22269033

      ,
      • Deerain J.
      • Druce J.
      • Tran T.
      • et al.
      Assessment of the analytical sensitivity of ten lateral flow devices against the SARS-CoV-2 omicron variant.
      The performance of other RADT brands is unknown as of the time of writing. Importantly, Bourassa and colleagues observed that SARS-CoV-2 specimens with a D399N nucleocapsid mutation were not detected by the SOFIA assay but were detected by the BinaxNOW test.
      • Bourassa L.
      • Perchetti G.A.
      • Phung Q.
      • et al.
      A SARS-CoV-2 nucleocapsid variant that affects antigen test performance.
      Thus, continued investigation on the part of the RADT manufacturers and independent researchers will be necessary to ensure that a given RADT brand continues to perform equivalently as new variants continue to emerge.

      Impact of Variants on Kinetics of Antigen Positivity

      An average of 4.3 days transpires between the beginning of viral shedding and peak viral load with the alpha variant (B1.1.7).
      • Jones T.C.
      • Biele G.
      • Mühlemann B.
      • et al.
      Estimating infectiousness throughout SARS-CoV-2 infection course.
      In contrast, the time from exposure to detection was reduced to 3 days with the Delta variant compared with 6 days for the wild-type strain.
      Viral infection and transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant - SARS-CoV-2 coronavirus/nCoV-2019 Genomic Epidemiology. Virological.
      Whether the shortened time it takes for variants to reach peak viral loads warrants a reconsideration of the frequency of serial RADT testing is currently unknown.

      Vaccine Breakthrough Cases

      Though vaccination reduces the incidence of both asymptomatic and asymptomatic infection even against variants,
      • Lopez Bernal J.
      • Andrews N.
      • Gower C.
      • et al.
      Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) variant.
      breakthrough cases with the Delta variant in vaccinated patients had initial Ct values that were indistinguishable from those occurring in unvaccinated individuals.
      • Brown C.M.
      • Vostok J.
      • Johnson H.
      • et al.
      Outbreak of SARS-CoV-2 infections, including COVID-19 vaccine breakthrough infections, associated with large public gatherings - Barnstable County, Massachusetts, July 2021.
      The duration of antigen positivity in vaccinated individuals has not been well defined; however, in a study with HCWs, culturable virus was less likely to be recovered from vaccinated HCWs with breakthrough Delta variant infection compared with unvaccinated infected HCWs at 68.6% versus 84.9%, respectively.

      Shamier MC, Tostmann A, Bogers S, et al. Virological Characteristics of SARS-CoV-2 Vaccine Breakthrough Infections in Health Care Worker. doi:10.1101/2021.08.20.21262158

      Whether antigen positivity mirrors culture positivity among vaccinated individuals with breakthrough infection remains to be determined.

      Public Health Reporting

      There is generally a lack of structured or automated result reporting to public health authorities for surveillance for many RADTs. In a Kaiser Health News survey, nearly half of US states indicated antigen test results are underreported.
      • Lauren Weber and Hannah Recht RP.
      Many states keep patchy data or don’t release results from antigen COVID tests, review shows. USA TODAY.
      This can lead to missed opportunities for contact tracing and inaccuracies in tracking positivity rates and potential outbreaks. Furthermore, laboratories are unable to easily follow-up on positive samples for sequencing. This may hamper efforts to detect and track potential variants of concern as they emerge.
      • Oude Munnink B.B.
      • Worp N.
      • Nieuwenhuijse D.F.
      • et al.
      The next phase of SARS-CoV-2 surveillance: real-time molecular epidemiology.

      Parting Thoughts

      The promise of antigen testing is fundamentally associated with its ability to democratize testing, enabling rapid detection of both asymptomatic and symptomatic infection alike and breakage of transmission chains. Nevertheless, the narrative of using RADTs to know one’s “infectious status” does not reflect the nuance of testing, that is, that such a status is not static and that transmission among individuals with low viral loads occurs. It is when RADT positivity and contagiousness match that they can have the greatest impact; however, it is often the case that there is a mismatch between the two .
      Although it has been proposed that RADTs be considered “public health tests” that are separate from their role as clinical diagnostics, they will invariably be used by symptomatic individuals for personal decision making because results have implications on the health of the test recipient. What has been fundamentally absent in the United States is concerted government-led education around how RADTs should be used and how results should be interpreted along with linkage to confirmatory and timely PCR testing. Unlocking the true power of this technology requires sufficient and cheap/free test supply and sufficient understanding among the general public of its limitations. This may be changing with the free distribution by the US government of RADTs to individuals who request them using an online portal.
      U.S. Department of Health & Human Services
      COVIDtests.gov - free at-home COVID-19 tests. COVIDtests.gov.
      As we have highlighted in this review, a multitude of data show that antigen testing works best when used as one element of a coordinated strategy involving vaccination and nonpharmacologic interventions, and not as the sole intervention. Indeed, there are no data published on the impact of frequent RADT surveillance in the absence of other public health measures.
      Ultimately, although the promise of antigen testing for SARS-CoV-2 comes from their massive scale, it has been frequently conveyed as if its power comes from individual decision-making. If the true potential of antigen testing is to be harnessed, society would do well to remember the original motto of the United States proposed by the founding fathers: “E pluribus unum,” or “out of many, one.” There is no singular solution to ending this pandemic, but certainly, the true power of antigen technology will come from its combination with other public health measures.

      References

        • Ranney M.L.
        • Griffeth V.
        • Jha A.K.
        Critical supply shortages - the need for ventilators and personal protective equipment during the Covid-19 Pandemic.
        N Engl J Med. 2020; 382: e41
        • Hanson Kimberly E.
        • Caliendo Angela M.
        • Arias Cesar A.
        • et al.
        Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19.
        (Available at:) (Accessed October 2, 2021)
      1. Scaling up COVID-19 rapid antigen tests: promises and challenges - the Lancet Infectious Diseases.
        (Available at:) (Accessed October 2, 2021)
        • Cevik M.
        • Tate M.
        • Lloyd O.
        • et al.
        SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.
        Lancet Microbe. 2021; 2: e13-e22
        • Prince-Guerra J.L.
        • Almendares O.
        • Nolen L.D.
        • et al.
        Evaluation of Abbott BinaxNOW rapid antigen test for SARS-CoV-2 infection at two community-based testing sites — Pima County, Arizona, November 3–17, 2020.
        MMWR Morb Mortal Wkly Rep. 2021; 70: 100-105
        • Pekosz A.
        • Parvu V.
        • Li M.
        • et al.
        Antigen-based testing but not real-time polymerase chain reaction correlates with severe acute respiratory syndrome Coronavirus 2 viral culture.
        Clin Infect Dis. 2021; (ciaa1706)https://doi.org/10.1093/cid/ciaa1706
        • Ginocchio C.C.
        • Zhang F.
        • Manji R.
        • et al.
        Evaluation of multiple test methods for the detection of the novel 2009 influenza A (H1N1) during the New York City outbreak.
        J Clin Virol. 2009; 45: 191-195
      2. Accuracy of rapid influenza diagnostic tests: a meta-analysis: Ann Intern Med: Vol 156, No 7.
        (Available at:) (Accessed October 2, 2021)
        • Merckx J.
        • Wali R.
        • Schiller I.
        • et al.
        Diagnostic accuracy of novel and traditional rapid tests for influenza infection compared with reverse transcriptase polymerase chain reaction.
        Ann Intern Med. 2017; 167: 394-409
        • Pinsky B.A.
        • Hayden R.T.
        Cost-effective respiratory virus testing.
        J Clin Microbiol. 2019; 57: e00373-19
      3. Rapid influenza diagnostic tests | CDC.
        (Available at:) (Accessed October 2, 2021)
      4. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: a living systematic review and meta-analysis.
        (Available at:) (Accessed October 2, 2021)
        • Lau L.L.H.
        • Cowling B.J.
        • Fang V.J.
        • et al.
        Viral shedding and clinical illness in naturally acquired influenza virus infections.
        J Infect Dis. 2010; 201: 1509-1516
        • Ip D.K.M.
        • Lau L.L.H.
        • Leung N.H.L.
        • et al.
        Viral shedding and transmission potential of asymptomatic and paucisymptomatic influenza virus infections in the community.
        Clin Infect Dis. 2017; 64: 736-742
        • Suess T.
        • Remschmidt C.
        • Schink S.B.
        • et al.
        Comparison of shedding characteristics of seasonal influenza virus (Sub)Types and influenza A(H1N1)pdm09; Germany, 2007–2011.
        PLoS One. 2012; 7: e51653
        • AF
        • BaligaChris
        • AklPascale
        • et al.
        Pre-procedural Covid-19 screening of asymptomatic patients: a model for protecting patients, community and staff during expansion of surgical care. NEJM catalyst innovations in care delivery.
        (Available at:) (Accessed October 2, 2021)
        • Krüger S.
        • Leskien M.
        • Schuller P.
        • et al.
        Performance and feasibility of universal PCR admission screening for SARS-CoV-2 in a German tertiary care hospital.
        J Med Virol. 2021; 93: 2890-2898
        • He X.
        • Lau E.H.Y.
        • Wu P.
        • et al.
        Temporal dynamics in viral shedding and transmissibility of COVID-19.
        Nat Med. 2020; 26: 672-675
        • Khoshchehreh M.
        • Wald-Dickler N.
        • Holtom P.
        • et al.
        A needle in the haystack? Assessing the significance of envelope (E) gene-negative, nucleocapsid (N2) gene-positive SARS-CoV-2 detection by the Cepheid Xpert Xpress SARS-COV-2 assay.
        J Clin Virol. 2020; 133: 104683
        • Chandler C.M.
        • Bourassa L.
        • Mathias P.C.
        • et al.
        Estimating the false-positive rate of highly automated SARS-CoV-2 nucleic acid amplification testing.
        J Clin Microbiol. 2021; 59: e0108021
        • Lin L.
        • Carlquist J.
        • Sinclair W.
        • et al.
        Experience with false-positive test results on the TaqPath real-time reverse transcription-polymerase chain reaction Coronavirus Disease 2019 (COVID-19) testing platform.
        Arch Pathol Lab Med. 2021; 145: 259-261
        • Health C for D and R
        Potential for false positive results with Abbott Molecular Inc. Alinity m SARS-CoV-2 AMP and Alinity m Resp-4-Plex AMP kits - Letter to clinical laboratory staff and health care Providers. FDA.
        (Available at:) (Accessed October 2, 2021)
        • Stokes W.
        • Berenger B.M.
        • Portnoy D.
        • et al.
        Clinical performance of the Abbott Panbio with nasopharyngeal, throat, and saliva swabs among symptomatic individuals with COVID-19.
        Eur J Clin Microbiol Infect Dis. 2021; : 1-6https://doi.org/10.1007/s10096-021-04202-9
        • Uwamino Y.
        • Nagata M.
        • Aoki W.
        • et al.
        Accuracy of rapid antigen detection test for nasopharyngeal swab specimens and saliva samples in comparison with RT-PCR and viral culture for SARS-CoV-2 detection.
        J Infect Chemother. 2021; 27: 1058-1062
        • Manabe Y.C.
        • Reuland C.
        • Yu T.
        • et al.
        Self-collected oral fluid saliva is insensitive compared with nasal-oropharyngeal swabs in the detection of severe acute respiratory syndrome Coronavirus 2 in outpatients.
        Open Forum Infect Dis. 2021; 8: ofaa648
        • Yokota I.
        • Shane P.Y.
        • Okada K.
        • et al.
        A novel strategy for SARS-CoV-2 mass screening with quantitative antigen testing of saliva: a diagnostic accuracy study.
        Lancet Microbe. 2021; 2: e397-e404
        • Health C for D and R
        In vitro diagnostics EUAs - antigen diagnostic tests for SARS-CoV-2. FDA.
        (Available at:) (Accessed October 2, 2021)
        • Peto T.
        • Affron D.
        • Afrough B.
        • et al.
        COVID-19: rapid antigen detection for SARS-CoV-2 by lateral flow assay: a national systematic evaluation of sensitivity and specificity for mass-testing.
        EClinicalMedicine. 2021; 36https://doi.org/10.1016/j.eclinm.2021.100924
      5. Protocol for evaluation of rapid diagnostic assays for specific SARS-CoV-2 antigens (lateral flow devices). GOV.UK.
        (Available at:) (Accessed October 2, 2021)
        • Perchetti G.A.
        • Huang M.L.
        • Mills M.G.
        • et al.
        Analytical sensitivity of the Abbott BinaxNOW COVID-19 Ag card.
        J Clin Microbiol. 2021; 59: e02880-20
        • Pickering S.
        • Batra R.
        • Merrick B.
        • et al.
        Comparative performance of SARS-CoV-2 lateral flow antigen tests and association with detection of infectious virus in clinical specimens: a single-centre laboratory evaluation study.
        Lancet Microbe. 2021; 2: e461-e471
        • Holzner C.
        • Pabst D.
        • Anastasiou O.E.
        • et al.
        SARS-CoV-2 rapid antigen test: fast-safe or dangerous? An analysis in the emergency department of an university hospital.
        J Med Virol. 2021; https://doi.org/10.1002/jmv.27033
        • Rhoads D.D.
        • Pinsky B.A.
        The truth about SARS-CoV-2 cycle threshold values is rarely pure and never simple.
        Clin Chem. 2021; : hvab146https://doi.org/10.1093/clinchem/hvab146
        • Richard-Greenblatt M.
        • Ziegler M.J.
        • Bromberg V.
        • et al.
        Quantifying the impact of nasopharyngeal specimen quality on severe acute respiratory syndrome coronavirus 2 test performance.
        Open Forum Infect Dis. 2021; 8https://doi.org/10.1093/ofid/ofab235
        • Singanayagam A.
        • Patel M.
        • Charlett A.
        • et al.
        Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19, England, January to May 2020.
        Euro Surveill. 2020; 25: 2001483
        • Walsh K.A.
        • Spillane S.
        • Comber L.
        • et al.
        The duration of infectiousness of individuals infected with SARS-CoV-2.
        J Infect. 2020; 0https://doi.org/10.1016/j.jinf.2020.10.009
        • Folgueira M.D.
        • Luczkowiak J.
        • Lasala F.
        • et al.
        Prolonged SARS-CoV-2 cell culture replication in respiratory samples from patients with severe COVID-19.
        Clin Microbiol Infect. 2021; 27: 886-891
        • Aydillo T.
        • Gonzalez-Reiche A.S.
        • Aslam S.
        • et al.
        Shedding of viable SARS-CoV-2 after immunosuppressive therapy for cancer.
        N Engl J Med. 2020; (NEJMc2031670)https://doi.org/10.1056/NEJMc2031670
        • Truong T.T.
        • Ryutov A.
        • Pandey U.
        • et al.
        Increased viral variants in children and young adults with impaired humoral immunity and persistent SARS-CoV-2 infection: a consecutive case series.
        EBioMedicine. 2021; 67: 103355
        • Jefferson T.
        • Spencer E.A.
        • Brassey J.
        • et al.
        Viral cultures for COVID-19 infectious potential assessment - a systematic review.
        Clin Infect Dis. 2020; : ciaa1764https://doi.org/10.1093/cid/ciaa1764
        • Wurtz N.
        • Penant G.
        • Jardot P.
        • et al.
        Culture of SARS-CoV-2 in a panel of laboratory cell lines, permissivity, and differences in growth profile.
        Eur J Clin Microbiol Infect Dis. 2021; 40: 477-484
        • Dinnes J.
        • Deeks J.J.
        • Berhane S.
        • et al.
        Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection.
        Cochrane Database Syst Rev. 2021; https://doi.org/10.1002/14651858.CD013705.pub2
      6. A tale of two tests: vermont town left puzzled by positive, then negative, COVID-19 results - the Boston Globe.
        (Available at:) (Accessed October 2, 2021)
        • Shah M.M.
        • Salvatore P.P.
        • Ford L.
        • et al.
        Performance of repeat BinaxNOW SARS-CoV-2 antigen testing in a community setting, Wisconsin, november-december 2020.
        Clin Infect Dis. 2021; : ciab309https://doi.org/10.1093/cid/ciab309
        • Pilarowski G.
        • Marquez C.
        • Rubio L.
        • et al.
        Field performance and public health response using the BinaxNOW TM Rapid SARS-CoV-2 antigen detection assay during community-based testing.
        Clin Infect Dis. 2020; : ciaa1890https://doi.org/10.1093/cid/ciaa1890
        • Van der Moeren N.
        • Zwart V.F.
        • Lodder E.B.
        • et al.
        Evaluation of the test accuracy of a SARS-CoV-2 rapid antigen test in symptomatic community dwelling individuals in The Netherlands.
        PLoS One. 2021; 16: e0250886
        • Kilic A.
        • Hiestand B.
        • Palavecino E.
        Evaluation of performance of the BD Veritor SARS-CoV-2 chromatographic immunoassay test in patients with symptoms of COVID-19.
        J Clin Microbiol. 2021; 59: e00260-21
        • Pray I.W.
        • Ford L.
        • Cole D.
        • et al.
        Performance of an antigen-based test for asymptomatic and symptomatic SARS-CoV-2 testing at two university campuses - Wisconsin, september-october 2020.
        MMWR Morb Mortal Wkly Rep. 2021; 69: 1642-1647
        • Young S.
        • Taylor S.N.
        • Cammarata C.L.
        • et al.
        Clinical evaluation of BD Veritor SARS-CoV-2 point-of-care test performance compared to PCR-based testing and versus the sofia 2 SARS antigen point-of-care test.
        J Clin Microbiol. 2020; 59: e02338-20
        • Ford L.
        • Whaley M.J.
        • Shah M.M.
        • et al.
        Antigen test performance among children and adults at a SARS-CoV-2 community testing site.
        J Pediatr Infect Dis Soc. 2021; (piab081)https://doi.org/10.1093/jpids/piab081
        • Eleftheriou I.
        • Dasoula F.
        • Dimopoulou D.
        • et al.
        Real-life evaluation of a COVID-19 rapid antigen detection test in hospitalized children.
        J Med Virol. 2021; 93: 6040-6044
        • Villaverde S.
        • Domínguez-Rodríguez S.
        • Sabrido G.
        • et al.
        Diagnostic accuracy of the panbio severe acute respiratory syndrome coronavirus 2 antigen rapid test compared with reverse-transcriptase polymerase chain reaction testing of nasopharyngeal samples in the pediatric population.
        J Pediatr. 2021; 232: 287-289.e4
        • Osterman A.
        • Baldauf H.M.
        • Eletreby M.
        • et al.
        Evaluation of two rapid antigen tests to detect SARS-CoV-2 in a hospital setting.
        Med Microbiol Immunol. 2021; 210: 65-72
      7. CDC. Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens for COVID-19. Centers for Disease Control and Prevention.
        (Available at:) (Accessed February 21, 2021)
        • Hogan C.A.
        • Huang C.
        • Sahoo M.K.
        • et al.
        Strand-specific reverse transcription PCR for detection of replicating SARS-CoV-2.
        Emerg Infect Dis. 2021; https://doi.org/10.3201/eid2702.204168
        • Binnicker M.J.
        Can testing predict SARS-CoV-2 infectivity? The potential for certain methods to be a surrogate for replication-competent virus.
        J Clin Microbiol. 2021; (JCM0046921)https://doi.org/10.1128/JCM.00469-21
        • Brümmer L.E.
        • Katzenschlager S.
        • Gaeddert M.
        • et al.
        Accuracy of novel antigen rapid diagnostics for SARS-CoV-2: a living systematic review and meta-analysis.
        PLOS Med. 2021; 18: e1003735
        • Hay J.A.
        • Kennedy-Shaffer L.
        • Kanjilal S.
        • et al.
        Estimating epidemiologic dynamics from cross-sectional viral load distributions.
        Science. 2021; 373https://doi.org/10.1126/science.abh0635
        • Tian D.
        • Lin Z.
        • Kriner E.M.
        • et al.
        Ct values do not predict severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) transmissibility in college students.
        J Mol Diagn. 2021; 23: 1078-1084
        • Marks M.
        • Millat-Martinez P.
        • Ouchi D.
        • et al.
        Transmission of COVID-19 in 282 clusters in Catalonia, Spain: a cohort study.
        Lancet Infect Dis. 2021; 21: 629-636
        • Wan Z.
        • Zhao Y.
        • Lu R.
        • et al.
        Rapid antigen detection alone may not be sufficient for early diagnosis and/or mass screening of COVID-19.
        J Med Virol. 2021; https://doi.org/10.1002/jmv.27236
        • Corman V.M.
        • Haage V.C.
        • Bleicker T.
        • et al.
        Comparison of seven commercial SARS-CoV-2 rapid point-of-care antigen tests: a single-centre laboratory evaluation study.
        Lancet Microbe. 2021; 2: e311-e319
        • Cevik M.
        • Marcus J.L.
        • Buckee C.
        • et al.
        Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) transmission dynamics should inform policy.
        Clin Infect Dis. 2021; 73: S170-S176
        • Larremore D.B.
        • Wilder B.
        • Lester E.
        • et al.
        Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening.
        Sci Adv. 2021; 7: eabd5393
        • See I.
        • Paul P.
        • Slayton R.B.
        • et al.
        Modeling effectiveness of testing strategies to prevent Coronavirus disease 2019 (COVID-19) in nursing homes—United States, 2020.
        Clin Infect Dis. 2021; 73: e792-e798
        • Smith R.L.
        • Gibson L.L.
        • Martinez P.P.
        • et al.
        Longitudinal assessment of diagnostic test performance over the course of acute SARS-CoV-2 Infection.
        J Infect Dis. 2021; 224: 976-982
        • Harmon K.
        • de St Maurice A.M.
        • Brady A.C.
        • et al.
        Surveillance testing for SARS-COV-2 infection in an asymptomatic athlete population: a prospective cohort study with 123 362 tests and 23 463 paired RT-PCR/antigen samples.
        BMJ Open Sport Exerc Med. 2021; 7: e001137
        • Ricks S.
        • Kendall E.A.
        • Dowdy D.W.
        • et al.
        Quantifying the potential value of antigen-detection rapid diagnostic tests for COVID-19: a modelling analysis.
        BMC Med. 2021; 19: 75
        • Schwartz K.L.
        • McGeer A.J.
        • Bogoch II,
        Rapid antigen screening of asymptomatic people as a public health tool to combat COVID-19.
        CMAJ. 2021; 193: E449-E452
        • García-Fiñana M.
        • Buchan I.E.
        Rapid antigen testing in COVID-19 responses.
        Science. 2021; 372: 571-572
        • Health C for D and R
        Potential for false positive results with antigen tests for rapid detection of SARS-CoV-2 - Letter to clinical laboratory staff and health care Providers. FDA.
        (Available at:) (Accessed October 2, 2021)
        • Pettengill M.A.
        • McAdam A.J.
        Can we test our way out of the COVID-19 Pandemic?.
        J Clin Microbiol. 2020; 58: e02225-20
        • Azzam Ihsan
        • Pandori Mark
        • Sherych Lisa
        Discontinue the use of antigen testing in skilled nursing facilities until further notice.
        (Available at:) (Accessed February 14, 2022)
        • Paltiel A.D.
        • Zheng A.
        • Sax P.E.
        Clinical and economic effects of widespread rapid testing to decrease SARS-CoV-2 Transmission.
        Ann Intern Med. 2021; 174: 803-810
        • University of Liverpool
        Liverpool Covid-SMART community testing Pilot evaluation Report.;.
        (Available at:) (Accessed October 4, 2021)
        • Kahanec M.
        • Lafférs L.
        • Schmidpeter B.
        The impact of repeated mass antigen testing for COVID-19 on the prevalence of the disease.
        J Popul Econ. 2021; : 1-36https://doi.org/10.1007/s00148-021-00856-z
        • Frnda J.
        • Durica M.
        On Pilot massive COVID-19 testing by antigen tests in Europe. Case study: Slovakia.
        Infect Dis Rep. 2021; 13: 45-57
        • Pavelka M.
        • Van-Zandvoort K.
        • Abbott S.
        • et al.
        The impact of population-wide rapid antigen testing on SARS-CoV-2 prevalence in Slovakia.
        Science. 2021; 372: 635-641
        • Moreno G.K.
        • Braun K.M.
        • Pray I.W.
        • et al.
        Severe Acute Respiratory Syndrome Coronavirus 2 transmission in intercollegiate athletics not fully mitigated with daily antigen testing.
        Clin Infect Dis. 2021; 73: S45-S53
        • Revollo B.
        • Blanco I.
        • Soler P.
        • et al.
        Same-day SARS-CoV-2 antigen test screening in an indoor mass-gathering live music event: a randomised controlled trial.
        Lancet Infect Dis. 2021; 21: 1365-1372
        • Llibre J.M.
        • Videla S.
        • Clotet B.
        • et al.
        Screening for SARS-CoV-2 antigen before a live indoor music concert: an observational study.
        Ann Intern Med. 2021; https://doi.org/10.7326/M21-2278
        • Tande A.J.
        • Binnicker M.J.
        • Ting H.H.
        • et al.
        SARS-CoV-2 testing prior to International Airline Travel, december 2020-may 2021.
        Mayo Clin Proc. 2021; https://doi.org/10.1016/j.mayocp.2021.08.019
        • Young B.C.
        • Eyre D.W.
        • Kendrick S.
        • et al.
        Daily testing for contacts of individuals with SARS-CoV-2 infection and attendance and SARS-CoV-2 transmission in English secondary schools and colleges: an open-label, cluster-randomised trial.
        Lancet. 2021; 398: 1217-1229
        • Pollock N.R.
        • Jacobs J.R.
        • Tran K.
        • et al.
        Performance and implementation evaluation of the Abbott BinaxNOW rapid antigen test in a high-throughput drive-through community testing site in Massachusetts.
        J Clin Microbiol. 2021; 59: e00083-21
        • Klein J.A.F.
        • Krüger L.J.
        • Tobian F.
        • et al.
        Head-to-head performance comparison of self-collected nasal versus professional-collected nasopharyngeal swab for a WHO-listed SARS-CoV-2 antigen-detecting rapid diagnostic test.
        Med Microbiol Immunol. 2021; 210: 181-186
        • McCulloch D.J.
        • Kim A.E.
        • Wilcox N.C.
        • et al.
        Comparison of unsupervised home self-collected midnasal swabs with clinician-collected nasopharyngeal swabs for detection of SARS-CoV-2 Infection.
        JAMA Netw Open. 2020; 3: e2016382
        • Haage V.
        • Ferreira de Oliveira-Filho E.
        • Moreira-Soto A.
        • et al.
        Impaired performance of SARS-CoV-2 antigen-detecting rapid diagnostic tests at elevated and low temperatures.
        J Clin Virol. 2021; 138: 104796
        • Frediani J.K.
        • Levy J.M.
        • Rao A.
        • et al.
        Multidisciplinary assessment of the Abbott BinaxNOW SARS-CoV-2 point-of-care antigen test in the context of emerging viral variants and self-administration.
        Sci Rep. 2021; 11: 14604
      8. Kanjilal S, Chalise S, Shah AS, et al. Analytic Sensitivity of the Abbott BinaxNOWTM Lateral Flow Immunochromatographic Assay for the SARS-CoV-2 Omicron Variant.; 2022. doi:10.1101/2022.01.10.22269033

        • Deerain J.
        • Druce J.
        • Tran T.
        • et al.
        Assessment of the analytical sensitivity of ten lateral flow devices against the SARS-CoV-2 omicron variant.
        J Clin Microbiol. 2021; 60 (e02479–21)
        • Bourassa L.
        • Perchetti G.A.
        • Phung Q.
        • et al.
        A SARS-CoV-2 nucleocapsid variant that affects antigen test performance.
        J Clin Virol. 2021; 141: 104900
        • Jones T.C.
        • Biele G.
        • Mühlemann B.
        • et al.
        Estimating infectiousness throughout SARS-CoV-2 infection course.
        Science. 2021; 373: eabi5273
      9. Viral infection and transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant - SARS-CoV-2 coronavirus/nCoV-2019 Genomic Epidemiology. Virological.
        (Available at:) (Accessed October 4, 2021)
        • Lopez Bernal J.
        • Andrews N.
        • Gower C.
        • et al.
        Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) variant.
        N Engl J Med. 2021; 385: 585-594
        • Brown C.M.
        • Vostok J.
        • Johnson H.
        • et al.
        Outbreak of SARS-CoV-2 infections, including COVID-19 vaccine breakthrough infections, associated with large public gatherings - Barnstable County, Massachusetts, July 2021.
        MMWR Morb Mortal Wkly Rep. 2021; 70: 1059-1062
      10. Shamier MC, Tostmann A, Bogers S, et al. Virological Characteristics of SARS-CoV-2 Vaccine Breakthrough Infections in Health Care Worker. doi:10.1101/2021.08.20.21262158

        • Lauren Weber and Hannah Recht RP.
        Many states keep patchy data or don’t release results from antigen COVID tests, review shows. USA TODAY.
        (Available at:) (Accessed October 4, 2021)
        • Oude Munnink B.B.
        • Worp N.
        • Nieuwenhuijse D.F.
        • et al.
        The next phase of SARS-CoV-2 surveillance: real-time molecular epidemiology.
        Nat Med. 2021; 27: 1518-1524
        • U.S. Department of Health & Human Services
        COVIDtests.gov - free at-home COVID-19 tests. COVIDtests.gov.
        (Available at:) (Accessed February 14, 2022)