Past COVID-19 infection offers protection against reinfection

Editor's Note

This systematic review and meta-analysis by researchers at the University of Washington, Seattle, finds that natural immunity provided by past COVID-19 infection offers strong protection against reinfection and severe disease for at least 40 weeks.

The analysis included 65 studies from 19 countries.

Among the findings:

• For those who had been infected with COVID-19, natural immunity against reinfection with severe disease was strong and long-lasting for all variants (90% for Alpha and Delta and 88% for Omicron BA.1 at 40 weeks after infection).
• Previous infection with pre-Omicron variants provided substantially lower protection against reinfection with Omicron BA.1 (74% at 4 weeks and 36% at 40 weeks after infection).
• The level and duration of protection against reinfection and severe illness is on a par with that provided by two doses of mRNA vaccines for Alpha, Delta, and Omicron BA.1 variants.

The immunity conferred by past COVID-19 infection should be weighed alongside protection from vaccination when assessing future disease burden, providing guidance on vaccination, and designing policies that mandate vaccination for workers, the researchers say.