“Reinfection can reasonably happen in three months or less,” said Jeffrey Townsend, the Elihu Professor of Biostatistics at the Yale School of Public Health and the study’s lead author. “Therefore, those who have been naturally infected should get vaccinated. Previous infection alone can offer very little long-term protection against subsequent infections.”…

Townsend and his team analyzed known reinfection and immunological data from the close viral relatives of SARS-CoV-2 that cause “common colds,” along with immunological data from SARS-CoV-1 and Middle East Respiratory Syndrome. Leveraging evolutionary principles, the team was able to model the risk of COVID-19 reinfection over time.

Reinfections can, and have, happened even shortly after recovery, the researchers said. And they will become increasingly common as immunity wanes and new SARS-CoV-2 variants arise.