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Researchers reported Wednesday that, in another twist to the debate about how best to protect children from the coronavirus, Covid vaccines offered reduced protection against hospitalizations among children 12 and older during the recent Omicron surge.

The efficacy of the vaccine against hospitalization remained stable in children aged 5 to 11 years and adolescents aged 12 to 18 years, but the two doses of the vaccine remained highly protective against critical illness requiring life support.

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

The data are largely consistent with studies showing that, in all age groupsvaccines lost a lot strength against infection With Omicron variant but still prevent serious illness and death.

A researcher at the Centers for Disease Control and Prevention, who led the study, Dr. Manish Patel said that while any hospitalization can be frustrating, it is reassuring that vaccines protect children from the worst consequences of infection.

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

As of March 23 only one of four children Slightly more than half of adolescents aged 5 to 11 and 12 to 17 years in the United States are fully vaccinated. These percentages have barely changed in the last few months.

For some parents still debating vaccination, the decision is complicated by the apparent withdrawal of the coronavirus. Cases and deaths fell lowest levels in a yearand no one knows yet if Omicron’s BA.2 sub-variant will bring another wave.

Some parents, believing their children’s risk of Covid to be insignificant, were reluctant to vaccinate them from the very beginning. But while children are much less likely than adults to become seriously ill, many more were hospitalized during the Omicron surge than at any other time in the pandemic.

In the new study, researchers analyzed medical records and interviewed parents of children ages 5 and older who were hospitalized for COVID. They excluded children who tested positive for the coronavirus but were hospitalized for other reasons.

Because relatively few children were hospitalized with Covid, the researchers were able to identify only 1,185 children and compared them to 1,627 other children who did not have Covid. Of 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 December 18, 2021, when the Delta variant was in circulation, and December 19 to February 17, when the Omicron variant was dominant. During the delta period, the efficacy against hospitalization among adolescents up to 44 weeks after vaccination was more than 90 percent.

However, during the Omicron surge, these numbers dropped sharply to about 40 percent for overall hospitalization protection, regardless of the time since vaccination.

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

The new study is among the first to examine vaccine efficacy in relation to disease severity among hospitalized patients. Eli Rosenberg, deputy director of science at the New York State Department of Health, said this trend is likely to occur in adult patients if they are analyzed similarly.

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

In children aged 5 to 11 years, full vaccination had a 68 percent effectiveness against hospitalizations overall. These data were collected during the Omicron surge because these children has become available only for vaccination on November 2. Few had to analyze efficacy based on disease severity.

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

Former Deputy Food and Drug Administration chief scientist Dr. Luciana Borio said the study suggests the vaccine protected most of these children from the worst outcomes.

“It really confirms the importance of vaccines for children ages 5 and up, and especially for those who are immunocompromised or have underlying medical conditions,” he said.

The Omicron variant can partially circumvent immune defense, so it’s not surprising that vaccines don’t do as well against the Delta variant, he and others said. Another recent study found that in adolescents aged 12 to 17 years, almost both doses of the vaccine no defense against moderate disease It is caused by the Omicron variant. (Booster doses are now recommended for all Americans aged 12 years and older.)

The large difference in vaccine efficacy between those who need life support and those who do not may be due in part to the wide variety of symptoms with which children are hospitalized. About one in four adolescents in the study required life-supportive interventions such as mechanical ventilation or extracorporeal membrane oxygenation.

Infectious diseases specialist at Yale School of Medicine, who was not involved in the study, Dr. Marietta Vazquez said from her own experience that most children hospitalized during the Omicron wave recovered quickly.

“The children we saw agreed—either they were very, very sick, or they were admitted mostly because they were infected and had a high fever or low oxygen saturation,” he said.

Noting that during the Omicron wave, parents seem more inclined to bring young children to the hospital, Dr. “There is a lot of anxiety and fear about Covid,” Vazquez said.

Some researchers have theorized that the decline in vaccine protection among adolescents is due to decreased effectiveness over time – meaning that adolescents may not have been so well protected during the Omicron surge because so much time had passed since their vaccines.

But the new study found that vaccine efficacy against the Omicron variant was 43 percent up to 22 weeks after vaccination and 38 percent between 23 and 44 weeks. Decreased immunity seemed less a factor than the variant itself.

Dr. “It looked more like Omicron,” Patel said.

Most of the vaccinated adolescents in the new study received only two doses. There were not enough people who received a third dose to evaluate its benefit, but a previous study suggested that a booster vaccine significantly improved protection against moderate disease in this age group. as in adults.

“I really think kids should get three doses, and I hope those numbers will increase,” said Akiko Iwasaki, an immunologist at Yale University. So far, only 14 percent of children 12 and older got a boost.