What is the difference between a booster and an additional dose?

A COVID-19 booster is given when a person has completed their vaccine series, and protection against the virus has decreased over time. Depending on the original series you had, some details will vary. Please review the booster eligibility information above and talk to your health care provider if you are not sure if you meet these guidelines. Please note, if you receive the Moderna booster, you will receive half of the original Moderna dose.

An additional dose is administered to people with moderately to severely compromised immune systems. This additional dose is intended to improve immunocompromised people’s response to their initial vaccine series. Depending on the original series given, some details will vary. Please review the additional dose eligibility information and talk to your health care provider if you are not sure if you meet these guidelines.