Yes. For immunosuppressed individuals, a series of three mRNA doses is now considered a “primary” series of vaccination against COVID-19. The CDC has approved a fourth dose, as a booster, that you can, and should, get three months after the third shot.

Existing vaccines likely do provide some immunity against omicron, the newest known variant of COVID-19, but boosters are important to maximize protection, according to a CDC statement issued when omicron was first detected in South Africa on Nov. 26, 2021. Omicron is now circulating in the United States and is variant has been labeled a “variant of concern” by the World Health Organization. It’s considered more contagious than earlier variants, though it’s not yet clear to what extent it poses risk of severe disease.