On Oct. 20, 2021, Moderna announced that the U.S. Food and Drug Administration (FDA) had authorized for emergency use a booster dose of the Moderna COVID-19 vaccine (mRNA-1273) at the 50 ﾵg dose level for people aged 65 and older; people aged 18 to 64 who are at high risk of severe COVID-19; and people aged 18 to 64 with frequent institutional or occupational exposure to SARS-CoV-2.

The booster dose was to be administered at least six months after completion of the primary series. The FDA also authorized a single booster dose of the Moderna COVID-19 Vaccine for individuals who had completed a primary vaccination with other authorized or approved COVID-19 vaccines.