Is there a role for SARS-CoV-2 antigen testing in the post-containment strategy?

With the availability and widespread deployment of antigenic tests for SARS-CoV-2 during the second epidemic wave in Europe, the performance of such tests in real-life situations is beginning to become available. The question of the role of these tests during periods of low circulation of the virus has been legitimately raised. We addressed this question by analyzing the results of more than 16,000 SARS-CoV-2 PCRs during the first half of 2020 in a French region heavily affected by COVID-19. We were thus able to calculate and extrapolate the theoretical sensitivity of the antigenic tests for various periods during and after the first epidemic wave. As the PCR-positivity rate of nasopharyngeal swabs declined over time, the proportion of samples with low Ct levels also decreased. Thus, the calculation of the analytical sensitivity of the antigenic tests ranged from 70 to 80% when the percentage of PCR positivity was > 1%, but fell below this score when it was lower. The performance and relevance of antigenic tests appears to be more limited during phases of low circulation of the virus. This may have a negative impact on the effectiveness of isolation, testing, and contact tracing strategies.