Moderately and severely immunocompromised people aged ≥18 years who completed an mRNA COVID-19 vaccine primary series and received an additional mRNA vaccine dose may receive a single COVID-19 booster dose (Pfizer-BioNTech, Moderna or Janssen) at least 6 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 is moderately or severely immunocompromised and has received two doses of an mRNA vaccine and ≥28 days has elapsed since the second dose, should receive an additional mRNA dose immediately (if Moderna COVID-19 vaccine is used, administer 100µg in 0.5ml), followed ≥6 months later by a single COVID-19 vaccine booster dose (if Moderna vaccine booster is used, administer 50µg in 0.25ml).
Source: cdc.gov/vaccines/covid-19/c...