The emergence of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), has led to a global pandemic with substantial societal and economic impacts on individual persons and communities. In the United States, more than 80 million cases and more than 986,000 COVID-19-associated deaths have been reported as of April 17, 2022. Persons of all ages are at risk for infection and severe disease. However, the risk for severe illness from COVID-19 is higher in people ages ≥50 years and those who are immunocompromised. Three COVID-19 vaccines are currently approved under a Biologics License Application or authorized under an Emergency Use Authorization (EUA) by the Food and Drug Administration (FDA) and recommended for primary vaccination by the Advisory Committee on Immunization Practices (ACIP): the two-dose mRNA-based Pfizer-BioNTech/Comirnaty and Moderna COVID-19 vaccines and the single-dose adenovirus vector-based Janssen (Johnson & Johnson) COVID-19 vaccine. On August 12, 2021, the FDA amended the EUAs for Pfizer-BioNTech (persons aged ≥12 years) and Moderna (persons aged ≥18 years) COVID-19 vaccines to authorize an additional dose for certain immunocompromised persons. Due to insufficient data, the EUA amendment for an additional dose did not apply to Janssen COVID-19 vaccine or to individuals who received Janssen COVID-19 vaccine as a primary series. Previous data on the use of additional doses of COVID-19 vaccine is linked here: EtR for Use of an Additional COVID-19 Vaccine Dose in Immunocompromised People | CDC. Additionally, during September-October, 2021, the FDA amended the COVID-19 vaccine EUAs to allow for booster doses of Pfizer-BioNTech, Moderna, or Janssen COVID-19 vaccines in persons who completed primary vaccination with these vaccines, as well as use of each of the available COVID-19 vaccines as a heterologous (or “mix and match”) booster dose in eligible individuals following completion of primary vaccination with a different COVID-19 vaccine. Previous data on the use of booster doses of COVID-19 vaccine is linked here: EtR for Use of COVID-19 Vaccine Booster Doses | CDC. On March 29, 2022, the FDA amended the COVID-19 vaccine EUAs to authorize a second booster dose of either the Pfizer-BioNTech or the Moderna COVID-19 vaccines for individuals 50 years of age and older as well as certain immunocompromised individuals 12 years of age and older at least 4 months after receipt of a first booster dose of any authorized or approved COVID-19 vaccine. Following FDA’s regulatory action on March 29, 2022, CDC updated its COVID-19 vaccination guidance to allow certain immunocompromised individuals and people over the age of 50 who received an initial booster dose at least 4 months ago to be eligible for another mRNA booster to increase their protection against severe disease from COVID-19. Separately, and in addition, based on newly published data, adults who received a primary vaccine and booster dose of Johnson & Johnson’s COVID-19 vaccine at least 4 months ago may now receive a second booster dose using an mRNA COVID-19 vaccine. Additional background information supporting the ACIP recommendation on the use of additional or booster doses of COVID-19 vaccine can be found in the relevant publication of the recommendation referenced on the ACIP website.