The CDC recommends a 3-dose primary mRNA COVID-19 vaccine for the primary vaccination for the moderately or severely immunocompromised persons aged ≥5 years; the third dose is given at a gap of at least one month after the second dose. This is followed by a booster dose for those aged ≥12 years.

In its updated guidance, the CDC has shortened the duration for booster dose following primary vaccination for immunocompromised persons.

The moderately or severely immunocompromised persons who have taken an mRNA covid-19 vaccine for the primary series are now advised to take a booster dose 3 months after the third dose for a total of four doses. The earlier recommended interval was 5 months. These recommendations apply to those who took the Moderna vaccine (≥18 years) as well as those who received the Pfizer-BioNTech vaccine (≥12 years).

Immunocompromised people who have received Johnson & Johnsons Covid-19 vaccine should preferably take a mRNA vaccine for the booster dose. A single booster dose is recommended at least two months after the second (additional) dose, for a total of 3 doses i.e.  one J&J vaccine dose followed by one additional mRNA vaccine dose at least 4 weeks later and then one booster dose.

Moderna vaccine should be used in a dose of 50 µg (0.25 mL) for the booster shot.

Source: Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Approved or Authorized in the United States, CDC. https://www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html#vaccination-people-immunocompromised