Oct 28, 2021 -- Some people with moderately or severely compromised immune systems may need a fourth dose of mRNA COVID-19 vaccine six months after a third shot, the U.S. Centers for Disease Control and Protection said this week in updated guidance.

It was only last August that the CDC authorized a third dose of vaccine for moderately and severely immunocompromised people, noting that they may not develop a full immune response from just two doses. Immunocompromised people who are fully vaccinated make up “a large proportion” of breakthrough cases needing hospitalization, the CDC says.

“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,” the CDC said in its updated guidance. “In such situations, people who are moderately and severely immunocompromised may receive a total of four COVID-19 vaccine doses.”

The CDC is not making a recommendation on a fourth “additional” dose -- which differs from a booster shot -- but urges people to discuss the possibility with their health care providers.

The CDC says severely or moderately immunocompromised people make up about 3% of the U.S. population. Falling under that definition are people receiving active cancer treatment for tumors or cancers of the blood, diagnosed with advanced or untreated HIV infection, undergoing active treatment with high-dose corticosteroids or other drugs that may suppress the immune response, and organ transplant and stem cell recipients.

The fourth-dose guidance doesn’t apply to people who received the Johnson & Johnson vaccine, which doesn’t use mRNA technology. Immunocompromised people who got the one-shot J&J vaccine should get a second shot of any approved vaccine at least two months after the first shot, the CDC says.

The CDC differentiates between “additional” shots and “booster” shots.

“An additional dose is administered to people with moderately to severely compromised immune systems,” the CDC says. “This additional dose of an mRNA COVID-19 vaccine is intended to improve immunocompromised people’s response to their initial vaccine series. A booster shot is administered when a person has completed their vaccine series, and protection against the virus has decreased over time.”

The CDC does not recommend immunocompromised people receive an additional dose plus a booster shot.

WebMD Health News Brief

Sources

The Centers for Disease Control: Considerations for use of a COVID-19 vaccine booster dose

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