Sunday it was reported that some immunocompromised people will be able to get a fourth shot soon. Starting later this week, some at-risk Americans become eligible for a 4th shot.

Some people with a weakened immune system can get a fourth dose of the coronavirus vaccine as early as this coming week, according to recommendations from the Centers for Disease Control and Prevention that were updated last week.

The C.D.C. endorsed a third dose of the Pfizer-BioNTech and Moderna vaccines for moderately or severely immunocompromised people on Aug. 13, but said this would be considered a part of the primary immunization, not a booster shot.

In October, the agency said those immunocompromised people could receive a booster shot — a fourth dose of vaccine, six months after their third dose. These guidelines were consistent with its recommendation for other adults.

Last week, hoping to stem the surge of infections with the highly contagious Omicron variant, the C.D.C. shortened that interval to five months for a booster shot for Pfizer-BioNTech or Moderna recipients.

For immunocompromised people who received a single shot of the coronavirus vaccine made by Johnson & Johnson, the C.D.C. does not recommend additional primary doses, but advises that they get a booster shot of the Moderna or Pfizer-BioNTech vaccines two months after the first dose.

Some people are born with absent or faulty immune systems, and in others, treatments for some diseases like cancer diminish the potency of immune defenses. The C.D.C. estimates there are about seven million immunocompromised individuals in the country.