A single shot of one of the currently authorized COVID-19 vaccines may be sufficient to provide immunity to individuals who have previously been infected by the virus, thus eliminating the need for a second dose and helping to stretch severely limited vaccine supplies, a study from Mount Sinai has found. Such a change in public health policy could also spare these individuals the unnecessary side effects of a second dose of vaccine, which researchers found to be significantly greater in individuals with pre-existing immunity to SARS-CoV-2, the virus that causes COVID-19. A letter to the editor was published today in the New England Journal of Medicine detailing the study.