On Mar. 31, 2022, the National Institutes of Health and Moderna announced a phase 2 clinical trial evaluating various additional COVID-19 booster shots had begun enrolling adult participants in the U.S. The trial aims to understand if different vaccine regimensﾗprototype and variant vaccines alone and in combinationsﾗcan broaden immune responses in adults who already have received a primary vaccination series and a first booster shot.

Despite waning protection against infection and mild illness during the Omicron wave, COVID-19 vaccines available in the United States so far have maintained durable protection against severe COVID-19. However, NIAID is preparing for the possibility of future variants evading protection against currently available COVID-19 vaccines.