3rd Shots Reduce Hospital Risk in Immunocompromised People, C.D.C. report says

Third shots of coronavirus significantly reduced the risk of immunocompromised people being hospitalized with Covid, the Centers for Disease Control and Prevention reported Thursday, reiterating the case for extra doses in that group.

The Pfizer-BioNTech and Moderna vaccines were about 88 percent effective against hospitalizations in immunocompromised people who received a third dose, compared to 69 percent more effective in immunocompromised people who received only two doses, the agency said.

The data comes from a study of people treated in 21 American hospitals from August to mid-December, a period when the Delta variant was prevalent. However, third doses have also been shown to increase people's defenses against serious effects from Omicron, even when overall protection against this variant is weaker.

The latest C.D.C. The study also added to the substantial evidence that third doses boost the defenses of people with stronger immune systems. Three doses of the Pfizer-BioNTech or Moderna vaccines were about 97 percent effective in preventing hospitalizations in this group, compared to 82 percent in recipients with two doses.

However, there are fewer studies on the real-world effects of additional doses in people with compromised immune systems. These people – the C.D.C. It is estimated that there are around seven million people in the country – who may be born with a defective immune system or, in other cases, experience weakened immunity as a result of treatments for diseases such as cancer.

Many of them produce fewer antibodies in response to vaccination or infection, leaving them vulnerable to the virus and at greater risk of serious illness.

In August, federal agencies approved a third dose of Pfizer-BioNTech or Moderna at least four weeks after the second dose for some immunocompromised individuals. The health authorities considered the additional dose for this group as an integral part of their primary vaccination course and not as a booster dose.

In October, the C.D.C. said immunocompromised people could receive a booster shot — a fourth dose of vaccine — as early as 2022 to improve or restore protection. But some of these people have said that pharmacies or hospitals have refused them the extra doses.

For immunocompromised individuals with a single dose of Johnson & Johnson vaccine, the C.D.C. recommends a top-up dose of the Moderna or Pfizer BioNTech shots.

The new study looked at around 1,100 adults with compromised immune systems and 1,900 other adults. The CDC said future studies should examine the protection that additional doses against the Omicron variant provide in immunocompromised individuals and the durability of that protection.