Does the Pfizer-BioNTech Covid-19 vaccine provide less protection to children aged 5 to 11 than to adolescents 12 to 17? A study from New York state released Monday suggests that’s the case. But new data from 10 states released Tuesday tell a different story.

The data, published by the Centers for Disease Control and Prevention, suggest that two doses of the Pfizer vaccine aren’t very protective against infection for either age group in the face of the Omicron variant, but that protection against severe illness appears to be holding up equally in both sets of children.

They do not suggest more rapid waning, or more marked waning, among the younger group of children.

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“When you look at the whole picture, we’re not seeing that signal that New York state is seeing,” Ruth Link-Gelles, the CDC’s program manager for Covid vaccine efficacy studies, told STAT in an interview.

In addition to the study, published in the CDC’s journal Morbidity and Mortality Weekly Report, the agency was to post statistics from other datasets on its website Tuesday afternoon. The various data sources tell the same story, Link-Gelles said. “They’re actually seeing very similar rates of disease among the 5- to 11-year-olds and the 12-to-15s. Where they see the difference is between the unvaccinated and vaccinated. ”

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On Monday, a preprint – a scientific paper that has not yet been peer-reviewed or published in a journal – was posted on a server by researchers with the New York State Department of Health.

Those data show a rapid and substantial decline in protection after vaccination in children in the younger age group, with efficacy against infections dropping off more quickly and dramatically than the declines seen in children aged 12 to 17. The study also found a significant, but less steep, decline in protection against hospitalizations.

The researchers noted a sharp difference in the protection seen in 11-year-olds and 12-year-olds, children on either side of the divide between the pediatric dose of the Pfizer vaccine and the adult dose. Adults get two shots 21 days apart; each jab contains 30 micrograms of vaccine; for the purpose of dosing, anyone 12 years of age and older is an adult. Children 5 to 11 get two doses on the same schedule, but their jabs contain one-third as much vaccine, 10 micrograms, as the adult dose.

“Our data support vaccine protection against severe disease among children 5-11 years, but suggest rapid loss of protection against infection, in the Omicron variant era,” the New York state researchers wrote. “Should such findings be replicated in other settings, review of the dosing schedule for children 5-11 years appears prudent.”

STAT requested an interview with Eli Rosenberg, the senior author of the New York state paper. But he was not made available.

In the study published by the CDC, vaccine effectiveness against emergency department or urgent care visits during the time when the Omicron variant was circulating was between 34% to 45% for adolescents ages 12 through 17 and 51% for children ages 5 through 11. Vaccination of children aged 5 through 11 only began in November so they were likely more recently vaccinated – with higher antibody levels – than children aged 12 to 17 during that period.

Kathryn Edwards, a vaccine expert at Vanderbilt University, said she is not yet convinced the dose used in 5- to 11-year-olds was too low. Rather, Edwards said, what’s clear from both studies is that in both the younger and older children, two doses of vaccine are not enough to fend off Omicron variant SARS-CoV-2 viruses.

“I do not think that there really are any data to suggest that the 5- to 11-year-olds is much worse off than the 12- to 15-year-olds, with the Omicron predominance,” Edwards said. “I think the better part of valor is to say that we need to look at data from more than a single source.”

“The data from New York suggested that there was poor protection for the 5- to 11-year-olds, but certainly this,” she said, referring to the CDC published paper, “would not suggest this.”

Both Edwards and Link-Gelles said more study, over a longer period of time, is going to be needed to get a true sense of how well the Pfizer vaccine is working in children. “I think it’s very early to be making the kind of conclusion that they did,” Link-Gelles said about the New York state paper.