This retrospective observational study aimed to gain a better understanding of the protective duration of prior SARS-CoV-2 infection against reinfection.The objectives were two-fold: to assess the durability of immunity to SARS-CoV-2 reinfection among initially unvaccinated individuals with previous SARS-CoV-2 infection, and read more to evaluate the crude SARS-CoV-2 reinfection rate and associated risk factors.During the pandemic era time period from February 29, 2020, through April 30, 2021, 144,678,382 individuals with SARS-CoV-2 molecular diagnostic or antibody test results were studied.
Rates of reinfection among index-positive individuals were compared to rates of infection among index-negative individuals.Factors associated with reinfection were evaluated using multivariable logistic regression.For both objectives, the outcome was a subsequent positive molecular diagnostic test result.
Consistent with prior findings, the risk of reinfection among index-positive individuals was 87% lower than the risk of infection among index-negative individuals.The duration of protection against reinfection was stable here over the median 5 months and up to 1-year follow-up interval.Factors associated with an increased reinfection risk included older age, comorbid immunologic conditions, and living in congregate care settings; healthcare workers had a decreased reinfection risk.
This large US population-based study suggests that infection induced immunity is durable for variants circulating pre-Delta predominance.