ABSTRACT
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.