Covid19-Sources

Conclusion 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.

In individuals with multiple infections, second infections were cleared more quickly than first infections. Furthermore, one’s relative speed of clearing infection roughly persisted across infections. Those with a relatively fast clearance speed in their first infection tended to have a relatively fast clearance speed in their second infection, and vice versa. Thus, while prior infection and vaccination can modulate a person’s viral kinetics in absolute terms, there may also exist some further immunological mechanism, conserved across sequential infections, that determines one’s strength of immune response against SARS-CoV-2 relative to others in the population.

A consistent finding between this and other studies on SARS-CoV-2 viral kinetics is that prior antigenic exposure, through infection or vaccination, tends to speed up viral clearance, and thus to reduce the duration of test positivity5,11,15. The duration of viral positivity has various consequences both for clinical management and for public health surveillance. For clinical management, test results should be interpreted in the context of a patient’s immune history, which can modulate both the extent and expected duration of viral shedding5,16. It may also be possible to adjust the recommended duration of post-infection isolation based on infection history.