Two of the COVID-19 vaccines currently approved in the United States require two doses, administered three to four weeks apart, however, there are few data indicating how best to minimize new infections and hospitalizations with limited vaccine supply and distribution capacity. A study published on 21st April, 2021 in the open access journal PLOS Biology by Seyed Moghadas at York University in Toronto, Canada, and colleagues suggests that delaying the second dose could improve the effectiveness of vaccine programs.