The updated (bivalent) boosters are called “bivalent” because they protect against both the original virus that causes COVID-19 and the Omicron variant BA.4 and BA.5.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.
Previous boosters are called “monovalent” because they were designed to protect against the single original virus that causes COVID-19. They also provide some protection against Omicron, but not as much as the updated (bivalent) boosters.
Two COVID-19 vaccine manufacturers, Pfizer and Moderna, have developed updated (bivalent) COVID-19 boosters. These updated boosters are expected to provide better protection against the virus and address waning vaccine effectiveness over time. The updated Pfizer-BioNTech booster for people is available for people 5 and older, and the updated Moderna booster is available for people 6 and older.
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.
The recommended vaccination schedule from the Centers for Disease Control and Prevention, including dosage, is available here.