By Molly Walker

Certain immunocompromised people can now receive, and in some cases should receive, a fourth dose of COVID-19 vaccine, the CDC said in updated interim clinical guidance this week.

"Moderately or severely immunocompromised" adults ages 18 and up who received an additional dose of Pfizer or Moderna's mRNA vaccines may now receive a booster dose of Pfizer, Moderna, or Johnson & Johnson at least 6 months after completing their third dose, the agency said.

They added that if a moderate to severely immunocompromised adult has received a two-dose series of Pfizer or Moderna, and more than 28 days has elapsed, that person should "immediately" receive an additional dose of Pfizer or the full-dose volume of 100 μg for Moderna, followed by a single booster dose with any of the three authorized vaccines at least 6 months later.

However, a moderate or severely immunocompromised "person who received one primary dose of [Johnson & Johnson] COVID-19 vaccine should not receive more than two COVID-19 vaccine doses," according to the guidance.

These individuals should receive a second dose of Pfizer, Moderna (at the booster dose volume of 50 μg) or Johnson & Johnson at least 2 months later. "A patient's clinical team is best positioned to determine the appropriate timing of vaccination," the recommendations said.

CDC noted the difference in the two recommendations, bolding the word "may" for those who received a primary series with mRNA vaccine and "should" for those who received a primary series with Johnson & Johnson.

This had been a topic of intense debate at a recent CDC Advisory Committee on Immunization Practices meeting, with CDC Director Rochelle Walensky, MD, noting that more specific recommendations about boosters in certain populations would be forthcoming.

In addition, the agency recommends individuals who developed myocarditis or pericarditis after a dose of mRNA vaccine should defer receiving a subsequent dose "until additional safety data are available."