Alliance for Pandemic Preparedness

March 18, 2021

Assessment of Protection against Reinfection with SARS-CoV-2 among 4 Million PCR-Tested Individuals in Denmark in 2020: A Population-Level Observational Study

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  • Individuals with a positive SARS-CoV-2 PCR test during the first surge in Denmark (prior to June 2020) were less likely to get a positive test during the second surge (September to December 2020) compared to individuals with a negative SARS-CoV-2 PCR test during the first surge. In this nationwide cohort study (n=525,339), 72 of 11,068 (0.65%) individuals who were initially positive retested positive again compared to 16,819 of 514,271 (3.27%) who were initially negative but retested positive, suggesting an estimated protection against a repeat infection of 80%. Among those aged 65 years and older, observed protection against a repeat infection was 47%. [EDITORIAL NOTE: Differences between those who do and do not retest for SARS-CoV-2 after an initial positive or negative test result could affect the observed test positivity. Conclusions based on these findings about the effectiveness of prior infection against re-infection should be made with caution.]

Hansen et al. (Mar 17, 2021). Assessment of Protection against Reinfection with SARS-CoV-2 among 4 Million PCR-Tested Individuals in Denmark in 2020: A Population-Level Observational Study. The Lancet. https://doi.org/10.1016/S0140-6736(21)00575-4