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CNN  — 

Many vaccinated kids experienced breakthrough infections during the Omicron surge, though protection against hospitalization remained stronger, a large new government-funded study found.

The study compared the vaccination status of children ages 5 to 17 who were treated for Covid-19 symptoms in emergency departments, urgent care centers and hospitals across 10 states between April 2021 and February 2022. Researchers reviewed records on nearly 40,000 clinic visits and 1,700 hospitalizations. The study was funded by the US Centers for Disease Control and published Tuesday in its Morbidity and Mortality Weekly Report.

The CDC study found vaccinated children ages 5 to 11 – the youngest and most recently vaccinated group – were about 46% less likely to have Covid-19 that resulted in care at an urgent care clinic or emergency room, compared with children who were unvaccinated.

However, the new study found vaccinated grade schoolers continued to be less likely to be hospitalized for their infections than children who were unvaccinated. Out of nearly 1,700 hospital admissions, there were 59 unvaccinated kids ages 5 to 11 admitted to the hospital after testing positive for Covid-19, and just two who were vaccinated. The study didn’t have enough cases to accurately estimate vaccine effectiveness against hospitalization in this age group.

The new study comes just a day after new data from the New York State Department of Health also found vaccine protection against Covid-19 dropped substantially for kids during the Omicron wave.

The Pfizer vaccine is the only Covid-19 vaccine authorized for people younger than 18.

Dr. Nicola Klein, an author of the study published Tuesday, thinks the dropoff in vaccine effectiveness in the younger age group wasn’t because the dose was too low or there was a big difference in response to the vaccines by age; she says this is just the rapid evolution of the virus.

“It is a little bit disheartening, but I think we also have to keep in mind that one of the complexities here is that because children started being vaccinated late last year, that coincides with when the Omicron variant began circulating,” said Klein, who is director of the Kaiser Permanente Vaccine Study Center.

The studies also come just as school districts around the country have started lifting mask mandates for students, and some parents and experts are left to wonder if it’s the right time to ease up on protections for kids.

“I don’t think it’s time to go free for all yet, but that, you know, if you know that everybody around you is vaccinated then I think you can relax a bit more,” said Dr. Robert Frenck, director of the vaccine research center at Cincinnati Children’s Hospital in Ohio. Frenck was not involved in the new research.

“So they don’t end up in the hospital themselves, but they come home to grandma and grandpa that maybe is immunocompromised and their immune system isn’t working that well and they give it to them. That would be my worry, too. As far as that people just kind of saying, oh, everything’s over, we can go back to normal. We’re not quite there yet.”

About 26% of kids ages 5 through 11 and 58% of those ages 12 through 17 have been fully vaccinated against Covid-19, according to the CDC.

Protection for adolescents and teens

Adolescents ages 12 through 17 – who get a dose of the Pfizer vaccine that’s three times higher than the shots for younger kids – had better protection against most circulating variants, the new study found, but that protection dropped off steeply with time and the arrival of the Omicron variant.

Five months or more after a second dose, kids in this age group had no significant protection against Omicron infections warranting a trip to the urgent care or ER. About a week after a booster shot, however, most of their protection appeared to be restored.

Boosted teens ages 16 to 18, were about 81% less likely to need to see a doctor for Covid-19.

Over the entire 11 months of the study, fully vaccinated adolescents – those ages 12 through 15 – were 83% less likely to be seen for Covid-19 at the emergency room or urgent care clinic and 92% less likely to be hospitalized until about 5 months after their second dose. After 5 months, vaccine protection dropped to just 38% for ER or clinic visits and 73% for hospitalizations in this age group.

Older teens, ages 16 through 17, were 76% less likely to be seen for Covid-19 in an ER or urgent care if the first five months after their second dose and 94% less likely to be hospitalized. After 5 months, their protection dropped to 46% for clinic visits and 88% for hospitalizations.

Boosters in the future?

The study was observational, meaning that the authors can’t prove cause and effect. Though the data was adjusted to try to account for meaningful differences between kids who were vaccinated and those who were not, the researchers say there could have been differences between these groups – such as the likelihood of masking or physical distancing – that might have influenced their results.

Still, the researchers note that it’s strong real-world data on how well the vaccines are protecting children. They say kids should stay up to date on their Covid-19 vaccines, including boosters for all children who are eligible. Currently, that group is adolescents ages 12 to 18 years of age.

Klein said she thinks it’s reasonable that boosters may soon be recommended for younger kids, too.

“We have pretty good evidence that the booster really increased the protection for 16- to 17-year-olds, and I think that’s shown pretty nicely in the paper, and I think it’s not unreasonable to expect that might be down the road for 5 to 11 year olds,” Klein said. “That’s certainly something that’s worth considering.”

Other experts who were not involved in the study agree.

“We know from the adults that the third dose did a lot. The third dose increased the effectiveness of the vaccine against Omicron it boosted all antibodies, including those key antibodies that still had some cross ability to neutralize Omicron,” said Dr. Jennifer Nayak, a pediatric infectious disease specialist at the University of Rochester Medical Center.

“So yes, for the kids as well, I think the third dose may be really important as the virus moves away from the protective immune response that was established by the vaccine,” Nayak said.

A booster dose for grade-school aged children is still likely to be months away. Pfizer is currently testing a booster dose for this age group, according to a spokesperson.

Experts who reviewed the studies but did not participate in the research said they shouldn’t cause parents to lose faith in the vaccines.

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“This is what you would expect in terms of mild illness,” said Dr. Paul Offit, director of the vaccine education center at the Children’s Hospital of Philadelphia. He pointed out that kids may catch Covid-19 even if they’re vaccinated, but the vaccines will keep them from the worst harms of the virus.

“The goal of this vaccine is to prevent severe illness,” said Offit, who says both studies show that the vaccines continue to keep kids out of the hospital.

What’s more, Offit says, these studies compare vaccinated kids to those who are unvaccinated, but they don’t account for children who may have already been infected by the virus and have some antibodies against future infection.

“So people who are considered unvaccinated may still at some level be protected, which means that your efficacy rate isn’t going to look as good,” he said. “None of these things are considered when they do these kinds of studies, so I think they tend to be falsely damning of the vaccine.”

Nadia Kounang, Jen Christiensen and Amanda Sealy and contributed to this report