The updated vaccine is called “bivalent” because it protects against both the original virus that causes COVID-19 and the Omicron variants. Omicron variants currently cause most cases of COVID-19 in the U.S., and the bivalent vaccine offers additional protection against these variants.
Previous vaccines were called “monovalent” because they were designed to protect against the single original virus that causes COVID-19. They also provided some protection against Omicron, but not as much as the updated, bivalent vaccine. The CDC now recommends updated, bivalent vaccine for everyone 6 months and older. The CDC has guidance for everyone 6 months and older based on age and medical condition.
The virus that causes COVID-19 has changed over time. The different versions of the virus that have developed over time are called variants. Learn more about variants of the COVID-19 virus.