Sometimes people who are moderately to severely immunocompromised do not build enough (or any) protection when they first get a vaccination. When this happens, getting another dose of the vaccine can sometimes help them build more protection against the disease, including COVID-19. Moderately or severely immunocompromised persons age 12 or older who received an initial mRNA COVID-19 vaccine primary series should receive an additional primary dose of the same mRNA COVID-19 vaccine at least 28 days after the second dose. The Johnson & Johnson vaccine is not included in the recommendation at this time.

In contrast, a booster dose refers to another dose of a vaccine that is given to someone who built enough protection after vaccination, but then that protection decreased over time and needs a boost. The Centers for Disease Control and Prevention has recommended booster doses for everyone 12 and older.

Moderately and severely immunocompromised people 12 or older who completed an mRNA COVID-19 vaccine primary series and received an additional mRNA vaccine dose should receive a single COVID-19 booster dose (Pfizer-BioNTech, Moderna or Janssen) at least 5 months after completing their third mRNA vaccine dose. In such situations, people who are moderately and severely immunocompromised may receive a total of four COVID-19 vaccine doses. A person who received one primary dose of Johnson & Johnson (Janssen) COVID-19 vaccine should not receive more than two COVID-19 vaccine doses. A patient’s clinical team is best positioned to determine the appropriate timing of vaccination.