Accuracy of Expired BinaxNOW Rapid Antigen Tests (preprint)

The widespread existence of expired antigen testing kits in households and potential coronavirus outbreaks necessitate evaluating the reliability of these expired kits. Our study examined BinaxNOW COVID-19 rapid antigen tests 27 months post-manufacture and 5 months past their FDA extended expiration dates, using SARS-CoV-2 variant XBB.1.5 viral stock. We conducted testing at two concentrations: the Limit of Detection (LoD) and 10 times the LoD. 100 expired and unexpired kits were tested at each concentration for a total of 400 antigen tests. At the LoD (2.32x10^2 TCID50/mL), both expired and unexpired tests displayed 100% sensitivity (95% CI 96.38% to 100%), with no statistical difference (95% CI -3.92% to 3.92%). Similarly, at 10 times the LoD, unexpired tests retained 100% sensitivity (95% CI 96.38% to 100%), while expired tests exhibited 99% sensitivity (95% CI 94.61% to 99.99%), demonstrating a statistically insignificant 1% difference (95% CI -2.49% to 4.49%, p=0.56). Expired rapid antigen tests had fainter lines than the unexpired tests at each viral concentration. The expired rapid antigens tests at LoD were only just visible. These findings carry significant implications for waste management, cost efficiency, and supply chain resilience in pandemic readiness efforts. They also provide critical insights for formulating clinical guidelines for interpreting results from expired kits. In light of expert warnings of a potential outbreak of a severity rivaling the Omicron variant, our study underscores the importance of maximizing the utility of expired antigen testing kits in managing future health emergencies.

Assessment of the Performance of Expired and Unexpired BinaxNOW COVID Rapid Antigen Test Kits Using Positive and Negative Controls (preprint)

Rapid antigen tests are widely used to diagnose infection with SARS-CoV-2, and millions of kits have been distributed for free by government agencies. However, unused and expired kits beyond their final expiration dates remain prevalent in people's homes. This study aimed to determine the accuracy of expired BinaxNOW COVID rapid antigen test kits. 100 expired and 100 unexpired test kits were checked for sensitivity and specificity using positive and negative controls, respectively. The results showed that there was no change in the sensitivity and specificity of BinaxNOW COVID rapid antigen test kits four months beyond the manufacturer-extended expiration date when using manufacturer-provided positive controls. The findings provide confidence in the accuracy of expired test kits, which could potentially reduce waste and strengthen supply chain resilience for pandemic preparedness. Further research utilizing actual human specimens can help determine the true accuracy of expired rapid antigen test kits in clinical use.

High Sensitivity and NPV for BinaxNOW Rapid Antigen Test in Children at a Mass Testing Site During Prevalent Delta Variant (preprint)

SARS-CoV-2 continues to develop new, increasingly infectious variants, such as delta and omicron. Here, we evaluate the efficacy of the Abbott BinaxNOW Rapid Antigen Test against the gold standard of Reverse Transcription Polymerase Chain Reaction (RT-PCR) in 1054 pediatric participants presenting to a state-owned high-volume Coronavirus Disease 2019 (COVID-19) testing site. During the testing period, the delta variant was predominant. Prior to sample collection, symptomatic and exposure status was collected for all participants based on Centers for Disease Control (CDC) criteria. RT-PCR results demonstrated an overall prevalence rate of 5.2%. For all participants, the sensitivity of the rapid antigen tests was 92.7% (95% CI 82.4% - 98.0%) and specificity was 98.0% (95% CI 97.0%-98.8%). For symptomatic participants, the sensitivity was 92.3% (95% CI 74.9% - 99.1%), specificity was 96.6% (95% CI 93.6%- 98.4%), positive predictive value (PPV) was 72.7% (95% CI 54.5% - 86.7%) and negative predictive value (NPV) was 99.2% (95% CI 98.2% - 100%). Among asymptomatic participants, the sensitivity was 92.6% (95% CI 75.7% - 99.1%), specificity was 98.6% (95% CI 97.5% - 99.3%) the PPV was 71.4% (95% CI 53.7% - 85.4%) and the NPV was 99.7% (95% CI 99.0% - 100%). Our reported sensitivity and NPV are higher than other pediatric studies, but specificity and PPV are lower. Importance Children are especially impacted by the disease and its ability to disrupt educational opportunities. Although vaccinations have been approved for children 5 years and older, many children remain unvaccinated. Widespread testing may improve the ability for children to remain in in-person activities, minimizing absences from school and extracurriculars. Highly accurate rapid antigen tests may be vital to containing future COVID-19 waves while mitigating detrimental effects.