Influence of Prior SARS-CoV-2 Infection on COVID-19 Severity: Evidence from the National COVID Cohort Collaborative

As SARS-CoV-2 has transitioned from a pandemic to endemic disease, the majority of new infections have been among previously infected individuals. To manage the risks and benefits of ongoing COVID-19 policies, it is important to understand whether prior infection modifies the severity of subsequent infections. Overall, prior infection was associated with a significant slightly elevated risk of severe disease. This effect varied month to month. As the pandemic proceeded, the effect of prior infection tended to evolve from generally protective during the pre-Omicron era to unprotective during the Omicron era. This points to the need for continued strategies to avert and minimize the harms of COVID-19, rather than relying upon immunity acquired through previous infection.