The FDA’s decision to authorize bivalent boosters was based on a wealth of evidence supporting the safety and efficacy of COVID-19 vaccines and boosters, including Omicron-targeted boosters. When BA.1 was still the predominant variant, vaccine manufacturers created a BA.1, Omicron-targeted vaccine. It was tested in human clinical trials with hundreds of participants and safely stimulated a strong immune response. However, the BA.1 variant was surpassed by other Omicron variants before the vaccine could be authorized. Currently, the Omicron variant BA.4 and BA.5 are causing most cases of COVID-19 in the U.S. and are predicted to circulate this fall and winter.
To make sure people can get boosters that protect against currently circulating variants, the FDA authorized the updated Moderna and Pfizer vaccines to help boost immunity against the original coronavirus strain and defend against the BA.4 and BA.5 Omicron variants. The FDA authorized the updated, bivalent boosters based on data from animal studies of the bivalent formula, human clinical trials of the BA.1-targeted formula, human clinical trials of the original monovalent vaccines and boosters, and extensive safety monitoring of existing COVID-19 vaccines. The Moderna and Pfizer bivalent boosters are both undergoing fully enrolled human clinical trials, and the data from these trials will be available before the end of the year.
The FDA has extensive experience with updated vaccines, like the annual influenza (flu) vaccine. The annual flu vaccine changes every year based on mutations in the flu virus. Like the virus that causes COVID-19, the flu virus changes over time. Flu vaccine manufacturers adjust their formula every year to protect against the dominant flu strain. Since these manufacturers use the same technology to make the vaccine each year, they are not required to conduct additional clinical trials.
The vaccine manufacturers of the bivalent boosters, Pfizer and Moderna are using the same technology they used to create their original COVID-19 vaccines to created updated boosters. The FDA worked very closely with the vaccine manufacturers to ensure the development of updated boosters was done safely and efficiently.