April 21, 2022

Rates of COVID-19 infection in unvaccinated adults with prior COVID-19

Editor's Note

This study from the University of Chicago finds that unvaccinated adults with prior COVID-19 infection had an 85% lower risk of acquiring COVID-19 again than unvaccinated adults without prior COVID-19.

The researchers analyzed data from patients tested for COVID-19 at 1,300 sites of care in 6 western states in the US.

Of 24,043 cases and 97,572 controls identified, 2,762 (2.8%) controls developed COVID-19, compared with 98 (0.4%) cases.

Prior COVID-19 infection was associated with protection of:

  • 85% against any recurrent COVID-19
  • 88% against hospitalization for COVID-19
  • 83% against COVID-19 not requiring hospitalization.

Protection remained stable over the study period (October 1, 2020 to November 21, 2021) with no attenuation up to 9 months after initial COVID-19 infection. This level of protection is similar to that of mRNA vaccines, but vaccine-associated protection wanes at 6 months.

The study findings may have important implications for vaccine policies and public health, the authors say.

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