While uncommon, COVID-19 reinfections happen, especially in people 65 years and older—underscoring the importance of continued physical distancing and prioritization for vaccines even in previously infected people, a large observational study yesterday in The Lancet suggests.
Researchers at the Statens Serum Institut in Copenhagen, Denmark, analyzed data on 10.6 million SARS-CoV-2 tests from 4 million Danes (69% of the population) from that country’s second COVID-19 surge, from Sep 1 to Dec 31, 2020. They then compared them with infection rates from residents with positive or negative tests during the first surge, March to May, 2020.
Before June 2020, 533,381 residents were tested, of whom 2.20% were positive for COVID-19. Of the 525,339 people eligible for follow-up during the second surge, 2.11% were infected during the first surge, and 0.65% tested positive again. In comparison, 3.27% of the 514,271 who had tested negative during the first surge were infected (adjusted relative risk [aRR], 0.195). Protection against reinfection was 80.5%.