Background: 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 .

Objectives: The question of the role of these tests during periods of low circulation of the virus has been legitimately raised . Study design: 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 .

Results: 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 .

Conclusions: 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.