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The Food and Drug Administration’s willingness to consider authorizing a Covid-19 vaccine developed by Pfizer and BioNTech for children under the age of 5 — without evidence yet that it would be protective — is raising concerns among some vaccine experts who fear the plan could backfire and undermine vaccine uptake in this group.

Pfizer and BioNTech confirmed Tuesday that they had been asked by the FDA to submit an application for the use of a two-dose vaccine in children 6 months to 4 years old. Data on a third shot would be submitted to regulators once they became available in the spring — ostensibly clearing the way for the agency to authorize a three-shot regimen for the youngest children who can get vaccinated. 

If the two-dose series is authorized by the FDA and the Centers for Disease Control and Prevention, potentially sometime this month, parents who want to vaccinate children under 5 could begin to do so before Pfizer has proven that the vaccine is protective for this entire age group — something that doesn’t normally happen.

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“It’s certainly a creative approach to trying to address the urgency that FDA and the White House is hearing from parents … for making these vaccines available for this younger age group,” said Jason Schwartz, an assistant professor of health policy at the Yale School of Public Health.

“But … the stakes are high and they’re never higher than for vaccines in this youngest age group, both for their effects on this vaccine and the effects on childhood vaccination and vaccine confidence generally.”

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Pfizer announced before Christmas that in a clinical trial of children aged 2 to 4 years old, two doses of vaccine failed to generate antibody levels on par with those seen in people aged 16 to 25 after two shots. Paradoxically, two doses given to infants aged 6 months to 23 months did generate antibody levels similar to those seen in the 16- to 25-year-olds, levels that are deemed to equate with protection.

In both groups of little kids, the vaccines appeared to be safe and the side effect profile was tolerable. Side effects included fever and chills, which are not uncommon reactions to vaccines in early childhood. 

The companies decided to test whether adding a third dose would raise antibody levels to required levels. But the data from the modified trial aren’t expected until late March and the FDA appears to be unwilling to wait until then. The agency’s independent vaccine expert panel, the Vaccines and Related Biological Products Advisory Committee, will meet Feb. 15 to review the data Pfizer is submitting with this application.

In emailed comments, the FDA said that given the recent increase in infections among children, it felt holding a public discussion about the risks and benefits of vaccination of this critical age group was important.

“The surge of the Omicron variant has rapidly facilitated the collection of important additional clinical data impacting the potential benefit-risk profile of a vaccine for the youngest children,” spokeswoman Abby Capobianco wrote. “In light of these new data and the rise in illnesses and hospitalization in this youngest age group, FDA believed that it was prudent to request that Pfizer submit the data it had available, including the data that it has recently collected during the Omicron surge.”

The idea of authorizing use of the first two doses while the third-dose data are pending is being framed as a way to allow parents eager to vaccinate children 4 and under to get a head start on the process, with a third dose to follow after review of the results of that part of the study.

None of the experts STAT spoke to for this article could recall a precedent for this approach. And several worried going down this path could erode willingness on the part of parents of young children to get them vaccinated. To date only about 20% of children aged 5 to 11 have received two doses of vaccine, according to CDC data.

“I don’t think authorizing two doses in children ages 2 to 4 years of age where effectiveness in this age group hasn’t been confirmed is going to convince the majority of parents to vaccinate their children,” said Norman Baylor, president and CEO of Biologics Consulting and a former head of the FDA’s Office of Vaccines. “If the vaccine in this age cohort is a three-dose vaccine, FDA should review the data from the three-dose series before authorizing the vaccine.”

In a poll released Monday by the Kaiser Family Foundation, 31% of parents of young children said they intend to have them vaccinated as soon as they are able. But 26% said they would not vaccinate children under the age of 5. A further 12% said they would only vaccinate their children if they were required to and 29% said they would take a “wait and see” approach.

Baylor said those results suggest following normal procedures would make more sense here. “The question is, where’s the fire?” he asked. “I think we can take a little time. If that third dose data is available in March, that’s not that long now.”

Schwartz has a vaccinated 8-year-old and a 2-year-old who was home from day care on Tuesday because a teacher tested positive for Covid. He suggested expediting the process for children 4 and younger will be welcomed by some parents, but won’t lead to a flood of vaccinated kids.

“To the extent that this is moving the clock ahead just by a few months, I think we should recognize that it will be a pretty limited number of families who will jump at this opportunity in the way that I have and in the way I probably would, depending on what the data look like,” he said.

Saad Omer, director of Yale University’s Institute for Global Health, said he understands concerns about what pursuing this plan could do to vaccine hesitancy among parents who aren’t convinced of the need to vaccinate children against Covid or the safety of the vaccines. But at this point, his expectations for vaccine uptake rates in children are not high.

“Childhood immunization coverage [for Covid] isn’t stellar anyway,” Omer said. “I don’t think this will particularly dent it.” 

Likewise, he wasn’t too concerned that this approach will provide ammunition to the burgeoning anti-vaccination movement. “The bottom line is contrarians will do what they do. That’s their schtick,” Omer said. “And anti-vaccine people will do what they always do.”

Malia Jones, an epidemiologist who teaches at the University of Wisconsin-Madison and who specializes in vaccine hesitancy, said it has been clear for a while that getting children vaccinated against Covid is going to be an uphill battle. She worries that the low level of confidence in Covid vaccines for children will erode parental support for other vaccines. “This is the thing that keeps me up at night,” she said.

“I think already it’s kind of a disaster for vaccine uptake in kids,” Jones said of the prospects for persuading parents to vaccinate their children against Covid and whether the FDA’s approach here will influence them. “Is it throwing gasoline on a dumpster fire? Maybe. But it was already a dumpster fire.”

This article has been updated with comment from the Food and Drug Administration. 

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