When the Food and Drug Administration gave emergency authorization to coronavirus vaccines from Pfizer and Moderna last December, it wasn't a hard decision. COVID-19 cases, hospitalizations and deaths were skyrocketing to record levels and public health officials were desperate to bring the pandemic under control. Clinical trial results showed both vaccines to be safe and highly effective in adults.
Now, as the FDA considers expanding authorization to young children, the U.S. finds itself in a very different stage of the pandemic, complicating how much data the agency will ask of vaccine makers and whether it will require standard approvals rather than emergency clearances. Dramatically reduced caseloads have shifted the risk-benefit balance, especially given emerging concerns over heart muscle inflammation in very small numbers of younger vaccine recipients.
These questions were debated at an FDA vaccines advisory committee meeting Thursday, during which some experts urged a go-slow approach to authorizing vaccines in children. Others warned cases could rebound as social distancing measures lift and coronavirus variants begin to spread.
"Before we start vaccinating millions of adolescents and children, it is so important to find out what the consequences are, because COVID-19 disease is disappearing in adolescents and children," said Cody Meissner, the director of pediatric infectious diseases at Tufts Medical Center.
The FDA convened the meeting to review the data that would support either an emergency use authorization, which the vaccines from Pfizer and partner BioNTech and Moderna have received, or a full approval.
Pfizer's vaccine received an EUA for 12- to 15-year-olds in May, while Moderna filed its application for 12- to 17-year-olds on Thursday. Trials are underway in younger age groups for both vaccines.
For those age groups, the companies didn't conduct the massively large efficacy trials as they did with adults, but instead took an "immunobridging" approach that evaluated whether the immune response seen in the adolescents matched that of adults, as well as measuring the safety of the vaccine.
A similar approach would likely be taken for the younger age groups. The main questions on which the FDA sought input was on what basis approval should be granted, as well as the size of the studies and the length of safety follow-up.
Countering Meissner, Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia, argued that vaccinating children as young as six months was necessary to bring the pandemic completely under control.
"We are going to have a highly vaccinated, highly immune population for years if not decades. It just seems silly to think that we're not going to have to include children as part of that," he said. "We still vaccinate children in this country for polio every year even though we haven't had a case of polio since the 1970s."
No consensus was reached on whether companies should pursue an EUA or standard approval for children younger than 12, leaving it to discussions between vaccine makers and the FDA on which path to take. The difference would likely be in the duration of the safety follow-up, which would be six months in the case of a full approval. For the vaccine EUA in adults, two months worth of safety follow-up was required.
FDA advisers gave some numbers on the enrollment necessary to assess immune response and safety, ranging from 1,500 to 10,000 study participants per age group.