Pfizer vaccine didn't protect kids well from omicron but did prevent severe disease, studies suggest

Two new studies suggest that COVID-19 vaccines didn't protect kids against omicron infections, though, as with adults, the shots seem to prevent serious disease.

Studies by Pfizer-BioNTech, which makes the only COVID-19 vaccine authorized for use in minors, found the shots were about 90% effective against infection. But those studies were conducted earlier in the pandemic, before the omicron outbreak.

The two newer studies tracked infections in December and January, as omicron was sweeping across the country, and provide the first real-world evidence of effectiveness against the coronavirus variant.

In one study, released Tuesday from the Centers for Disease Control and Prevention, two doses of the Pfizer-BioNTech vaccine provided strong protection – 74% to 94% – against emergency department visits for older adolescents. But the vaccine was not particularly effective at preventing them from becoming infected with COVID-19 and effectiveness faded after the shots.

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While teens were more likely to be hospitalized during the delta outbreak last fall, more children ages 5-11 were hospitalized during omicron, according to the study, which tracked serious infections among otherwise healthy children in 10 states from April 2021 through January.

Protection faded substantially after six months, the study showed, but a booster dose, authorized for older adolescents, restored the effectiveness.

In the second study, released Monday from New York state, researchers examined data from more than 1.2 million vaccinated children ages 5 to 17.

Vaccination prevented 76% of infections within two weeks of full vaccination for 12- to 17-year-olds, but just 56% of infections at a month after vaccination. For children ages 5 to 11, protection against mild disease fell from 65% to 12% by one month after vaccination, according to that study, which has not yet been peer reviewed.

Throughout the pandemic, older adults have been more vulnerable to severe COVID-19 infections than children, with risk roughly declining with age. Still, 114,000 children have been hospitalized with COVID-19 in the United States during the pandemic and just under 1,000 children ages 5 and up have died.

The numbers of vaccinated children hospitalized in New York state from mid-December through January, the period covered in the study, was too small to draw firm conclusions about the vaccine's effectiveness in preventing hospitalization and death, said Dr. Eric Rubin, an infectious disease specialist at the Harvard T.H. Chan School of Public Health and editor-in-chief of the New England Journal of Medicine.

"My strong suspicion is the vaccine will work to prevent severe disease in these kids if you had a large enough sample size," said Rubin, who also sits on an expert advisory panel to the Food and Drug Administration. "This study is consistent with that idea."

Vaccines are only authorized for children ages 5 and up. Studies in children ages 2 to 4 showed that two shots were not effective at preventing infection. Last month, federal officials delayed consideration of the vaccine for the youngest children, hoping that data from a third shot would be more convincing of the vaccine's effectiveness.

A booster shot does appear to be extremely safe, according to another study published Tuesday by the CDC, which showed that among 12- to 17-year-olds side effects were less severe and shorter-lasting with the third dose than the second.

Children ages 12 and up receive the same 30-microgram dose of the Pfizer-BioNTech vaccine as adults, while children ages 5 to 11 receive a 10-microgram dose and the youngest children have been tested on a 3-microgram dose. It's possible that higher doses would be more effective, experts said, but Pfizer-BioNTech went with lower doses to reduce side effects, including fever.

Regardless of the dose, it's possible that a third dose would better protect children against omicron, experts said. Studies in adults have shown that a third shot provides much more protection against the variant, though two doses does seem to prevent most severe disease.

Dr. Cody Meissner, who heads the division of pediatric infectious diseases at Tufts Children's Hospital in Boston, said the New York study will make it harder for parents to decide whether to vaccinate their children against COVID-19.

The likelihood of benefit from the shots is low, he said, because the risk of severe disease is already so low in children, particularly younger ones.

Still, he said, if children have weakened immune systems or live with an older or vulnerable relative or in an area of high COVID-19 transmission, vaccination likely makes sense.

"Each parent has to make her or his own decision about whether they want to vaccinate their child," Meissner said. "A perfectly healthy child is very, very unlikely to be hospitalized with COVID-19 – that doesn't mean it's zero, but you have to think carefully about what's in the best interest of the child."

Dr. Ofer Levy, director of the Precision Vaccines Program at Boston Children's Hospital, said he thinks the federal recommendations to vaccinate all eligible children still makes sense. His own three kids have received their shots, he said.

But the New York study shows that the age of the child matters, as does the variant, the dose and the number of doses given, he said.

Dr. Paul Offit, who directs the Vaccine Education Center at Children's Hospital of Philadelphia, said he's neither surprised nor concerned about the results. Vaccines were always intended to prevent severe disease, not mild illness, he said, and studies in adults had shown that "omicron is immune evasive."

Offit, who also sits on the FDA advisory panel, said the New York study doesn't go "granular" enough to know whether the vaccinated children who were hospitalized needed care because of COVID-19 or if a mild infection was simply detected once they were admitted.

The bottom line is the vaccines do help protect kids, even if not as well as people had hoped, Rubin said.

"It is disappointing that at least two doses of vaccine don't last very long, but it's still better than nothing," Rubin said. "There is a real benefit. It's totally measurable. And the risk seems to be extraordinarily low."

Contact Weintraub at kweintraub@usatoday.com.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Pfizer's COVID vaccine effectiveness in kids faded amid omicron surge