FDA asks Pfizer, Moderna to test vaccines in more children to help rule out safety issues

Federal regulators have requested that vaccine companies expand their trials to test coronavirus shots in several thousand school-aged children before seeking authorization—a move intended to assess whether a rare inflammation of the heart muscle that has been seen in young adults shortly after vaccination is more common in younger age groups.

The changes to ongoing pediatric trials run by Moderna and Pfizer and its German partner, BioNTech, could delay the availability of the vaccines to children between 5 and 11 beyond the hoped-for timeline of early fall, although it is unclear by how much. As the country faces a surge fueled largely by cases in unvaccinated people and the school year approaches, pediatricians and families have impatiently awaited shots of protection.

At a CNN town hall meeting last week, President Biden said that children under 12 might have access to a vaccine “soon,” but the regulatory decision to increase the trial size will mean recruiting and vaccinating many more children.

A federal official who spoke on the condition of anonymity predicted that authorization of a coronavirus vaccine for children 5 through 11 might come by late October or early November. The government is not expecting it will be a big problem to enroll more children because so many parents are eager to get their children vaccinated, the official said.

Ray Jordan, a spokesman for Moderna, said that the company was “actively discussing a proposal” with federal regulators to expand its trial, but had not settled on final numbers yet. He predicted that authorization could occur in “winter 2021/early 2022.”

“The objective is to enroll a larger safety database which increases the likelihood of detecting rarer events,” Jordan said in an email. The original trial included nearly 7,000 children from 6 months to 12 years old.

Jerica Pitts, a spokeswoman for Pfizer, said that the company hasn’t yet made any updates to its trial design or its timeline, which was originally predicted to report results in September for children ages 5 to 11, with results for children ages 2 to 5 expected to follow shortly and for children as young as 6 months in October or November.

Pfizer originally designed its trial to include 4,500 children from 6 months to 12 years old. Two-thirds would receive the vaccine, and the rest would receive a placebo.

At a Food and Drug Administration advisory committee meeting last month, several experts said that they would expect the pediatric trials to be larger, although there was no consensus on a number.

The FDA wants to be particularly careful about the possibility of children developing myocarditis, or heart inflammation, after receiving a coronavirus vaccine. Adolescents who receive the vaccines are more likely to develop myocarditis than adults—though the risk remains small—and officials want to increase the chances that the trials will indicate whether there is increased incidence of heart inflammation in children.

Myocarditis and pericarditis, inflammation of the heart or surrounding tissue, has rarely occurred after vaccination with both vaccines and is considered by the Centers for Disease Control and Prevention “likely” associated with the shots. The most common symptom is chest pain. The CDC said in June that there had been more than 1,200 cases of heart inflammation out of about 300 million mRNA doses administered in the United States at that time and the cases were more frequent in young males. The risks of covid-19 are greater than the rare risk from vaccination and people typically recover, the CDC said.

The FDA is likely to require two months of follow-up data for the 5-to-11 age group, as it did for adults and adolescents. For children under 5, the agency might require four to six months of follow-up data, meaning vaccines are unlikely to be available for several months for infants and young children.

FDA spokeswoman Abigail Capobianco said in an email that while the agency couldn’t comment on specific interactions with companies, “we do generally work with sponsors to ensure the number of participants in clinical trials are of adequate size to detect safety signals.”

David Benkeser, a statistician who works on clinical trials at Emory University’s Rollins School of Public Health, said that increasing the trial size would be helpful to identify any potential safety signals.

“In terms of timelines, it will definitely push timelines back,” Benkeser said in an email, noting that how much of a delay will occur depends on how fast the trials are recruiting participants. But after that, it would likely take about four to five weeks to deliver shots to participants and then two weeks to measure their immune responses.

The agency has not decided what it will require for trials for children under 5. The decisions will partly will depend on whether the data for the older children is clear and does not indicate any safety problems, said a federal official, who spoke on the condition of anonymity because they were not authorized to speak publicly.

The official also emphasized that an urgent administration priority is granting the Pfizer vaccine full approval—perhaps by the end of the summer.

The individual said that a full approval could mean an additional 25 million people would end up getting vaccinated—5 million who might not have accepted the vaccine until final approval and an additional 20 million who might be covered by mandates issued by colleges, universities and the military.