Covid Live Updates: News on Boosters and the Omicron Subvariant

In yet another twist to the debate over how best to protect children against the coronavirus, researchers reported on Wednesday that Covid vaccines conferred diminished protection against hospitalization among children 12 and older during the latest Omicron surge.

Vaccine effectiveness against hospitalization held steady in children aged 5 to 11 years, however, and among adolescents ages 12 to 18 years, two doses of the vaccine remained highly protective against critical illness requiring life support.

But effectiveness against hospitalization for less severe illness dropped to just 20 percent among these children. The findings were published in the The New England Journal of Medicine.

The data are broadly consistent with studies showing that, across all age groups, the vaccines lost much of their power against infection with the Omicron variant but still prevented severe illness and death.

Among adolescents in the study who were critically ill, 93 percent were unvaccinated, and most had at least one underlying condition, Dr. Patel noted. “I think the big take-home message is that with the simple act of vaccination, you can prevent most critical illness in most children,” he said.

As of March 23, only about one in four children ages 5 to 11, and just over half of adolescents 12 to 17, were fully vaccinated in the United States. Those percentages have barely budged in the past few months.

Because relatively few children are hospitalized for Covid, the researchers were able to identify only 1,185 children, comparing them with 1,627 others who did not have Covid. Among those hospitalized for Covid, 291 received life support and 14 died.

The study included data from 31 hospitals in 23 states, and spanned July 1 to Dec. 18, 2021, when the Delta variant was circulating, and Dec. 19 to Feb. 17, when the Omicron variant was dominant. During the Delta period, effectiveness against hospitalization was more than 90 percent among the adolescents up to 44 weeks after immunization.

When the researchers parsed the data by severity of illness, they found that vaccine effectiveness against critical illness among hospitalized adolescents remained high, at 79 percent, but had fallen to 20 percent for less severe illness.

The new study is among the first to look at vaccine effectiveness in relation to severity of illness among hospitalized patients. It’s possible that this trend would appear among adult patients, too, if they were analyzed similarly, said Eli Rosenberg, deputy director for science at the New York State Department of Health.

“This split along critical, noncritical is interesting,” he said. “This definitely adds a new layer.”

About 78 percent of all hospitalized adolescents in the study, and 82 percent of younger children, had one or more underlying medical conditions, like obesity, autoimmune diseases or respiratory problems, including asthma.

The study suggests that the vaccine protected a majority of these children from the worst outcomes, said Dr. Luciana Borio, a former acting chief scientist at the Food and Drug Administration.