As the Delta variant ravages the Southeast and threatens similarly dire outcomes in broad swaths of the country, businesses, government bodies, health groups, and schools have begun mandating employees prove they are vaccinated against COVID-19. Workplace vaccination mandates are a legal, ethical and necessary means to increase population-level immunity and protection against infection.
But such mandates beg the question: What about people who already had the coronavirus? Before vaccines for COVID-19 were available, many scientists suspected that prior infection protected against re-infection, as shown in experiments in animals or from studies of human outbreaks.
More recently, a not-yet-peer-reviewed study conducted this year among 52,238 employees of the Cleveland Clinic Health System in Ohio found that of 1,359 unvaccinated people, zero previously-infected employees developed COVID-19. Meanwhile, among those unvaccinated without prior SARS-CoV-2 infection, there was a steady rate of new infection.