FDA: Pfizer, Moderna vaccines for kids under 6 are safe, effective

Two Covid-19 vaccine options for babies and toddlers are safe and effective, FDA reviewers said in briefing documents posted online over the weekend, setting the stage for regulators to potentially authorize the shots for emergency use later this week.

The three-dose Pfizer-BioNTech vaccine for kids ages 6 months through 4 years will likely benefit this age group, the FDA said, noting higher hospitalization and death rates among the youngest children in the U.S. compared with those 5 and older.

"Given the uncertainty of the COVID-19 pandemic and likelihood of continued SARS-CoV-2 transmission during the ensuing months, deployment of the vaccine for use among children 6 months through 4 years of age will likely have a beneficial effect on COVID-19 associated morbidity and mortality in this age group," the agency said.

Moderna's two-dose Covid-19 vaccine regimens for children are generally safe and effective for children ranging in age from 6 months to 17 years old, the FDA said in a separate briefing document posted late Friday.

Background: The documents are the products of months of review of the companies' safety and immunogenicity data, which federal regulators must independently verify. They'll form the basis of the FDA's independent vaccine advisers' review at meetings Tuesday and Wednesday, during which they'll vote on whether to recommend the agency endorse EUAs for the myriad age groups.

The first meeting will focus on Moderna's proposed vaccine series for children 6 years through 17 years, while the second day will cover both companies' bids to vaccinate the country's youngest children, down to 6 months old.

Limited data on efficacy: The FDA analyzed the vaccines' ability to induce neutralizing antibody responses in kids that were comparable to young adults, a concept known as immunobridging. Both met the agency's success criteria.

Real-world efficacy against the Omicron variant in the 6-month-to-5-year-old age group for Moderna's vaccine ranged from 36 to 51 percent, but efficacy estimates for all age groups were "generally consistent" with rates seen in observational studies of adults during the same variant waves, the FDA said.

Preliminary analyses of the Pfizer vaccine's efficacy in kids under 5 of 80 percent against disease, though only 10 Covid cases were reported among study participants before the data cutoff date in April.

There were still plenty of efficacy unknowns in both companies' data that reflect the current state of adult vaccination in the U.S., including duration of effectiveness and how well vaccination protects against outcomes like long Covid, the FDA said. Children will likely need booster doses in the future, given adults' experience with waning antibody protection, reviewers said.

Adverse reactions like headaches and fatigue were more common in teens than in younger kids, likely because they received larger vaccine doses, the FDA said. Fever was reported more frequently among the youngest vaccine recipients.

No new safety signals were detected in the companies' clinical trials, though they were unlikely large enough to detect the rarest of side effects, FDA said.

The FDA's reviews of the companies' data come after months of angst from parents who felt strung along by statements that Covid-19 vaccines would be available for the country's youngest children by early 2022, only to see dates shift. The FDA scheduled an advisory committee meeting in February to consider a two-dose primary series of Pfizer's vaccine, only to pull back once the data suggested a third dose could bolster its effectiveness.

Parents and advocates for children under 5 to get access to vaccines erupted over a POLITICO report in April that the Biden administration was leaning toward authorizing both Pfizer-BioNTech's and Moderna's products at the same time to make it easier to promote the shots, a move some believed resulted in regulators sitting on Moderna's application while Pfizer continued to collect data and complete its submission. FDA Commissioner Robert Califf later insisted there would be no holdup on Moderna's application, but the advisory committee meeting schedule ultimately ensured both vaccines would be considered head-to-head.

Myocarditis shift: No cases of myocarditis or pericarditis — inflammation of the heart muscle or lining, respectively — were reported in Moderna's pediatric trials. Both conditions are known risks of Covid-19 messenger RNA vaccines, particularly among males ages 12 to 39.

Data from international vaccine safety surveillance programs have suggested that a higher rate of the heart conditions occurs after immunization with Moderna's shots than with Pfizer-BioNTech's, which, along with the availability of the Pfizer vaccine for adolescents, convinced the FDA last fall not to move forward with an EUA then for 12- to 17-year-olds, the agency said in the briefing document.

But analyses of U.S. data in active and passive surveillance systems conducted in April and May "do not support a difference in myocarditis/pericarditis risk for [Moderna] as compared to [Pfizer-BioNTech] or suggest a small difference because of uncertainties," the FDA said, later calling evidence of a risk difference between the two products "inconclusive."

The benefit-risk balance of allowing Moderna's vaccine as an option for teens amid heart inflammation concerns is likely to be a major source of debate during Tuesday's meeting.

Neither condition was reported in Pfizer and BioNTech's trials for kids under 5 years old, and the risk for that age group is unknown. The risk for vaccine-associated myocarditis for that age group may be lower compared with older teens, given the lower rate seen in males ages 5 to 11 years as well as lower rates of adverse reactions among the youngest kids, the FDA said.