Here are the three main issues the FDA panel considered at its meeting:
Safety
The committee mainly focused on assessing whether the vaccines are safe for children, and the potential protective gains to kids and society as a whole if they are ultimately put into use for the youngest Americans.
One big consideration for regulators: Children’s developing immune systems appear to react to Covid-19 differently than do those of adults. Kids are generally less likely to develop severe Covid-19 than are adults — but a small percentage develop a serious inflammatory syndrome called MIS-C that adults do not.
Over 300 children in the US have been hospitalized from the disease, and recent data from the Centers for Disease Control and Prevention show that hospitalizations are increasing. Children under 5 and teens have higher rates of hospitalization than kids 5 to 11, according to federal data.
“We’re going to have to have a highly vaccinated or highly immune population for years, if not decades, and it just seems silly to think we’re not going to have to include children as part of that,” said Paul Offit, a pediatrician at the Children’s Hospital of Philadelphia.
Others were more cautious. Cody Meissner, professor of pediatrics at Tufts University School of Medicine, said kids need a safe and effective Covid shot — but argued against authorizing one for emergency use in anyone under 18, saying the safety data currently available is insufficient.
“The burden of disease is so small and the risks are just not clear,” he said.
And while clinical trials are designed to sniff out common side effects, some rarer conditions linked to vaccination may only appear once a shot is in wide use. Federal health agencies are now looking into reports of heart inflammation in some people under 30 who received the mRNA vaccines from Moderna and Pfizer.
Though the conditions are rare, CDC has found more cases occurring after the second shot of an mRNA vaccine, with early data showing about 16 cases per million second doses.
The panel debated whether it’s more important to test a large cohort of children or to track their immune response over a long period of time. “We’re not seeing more adverse events later on,” said Hayley Gans, a pediatrician at Stanford University, of Covid vaccine trials. She’s rather see larger studies over a shorter period of time to rule out even the rarest adverse events, like heart inflammation.
Other committee members acknowledged the uncertainty around how Covid may spread once fall and winter arrive, and people in a wide swath of the country begin spending more time indoors. Panel experts expressed concern about not having an immunization option for younger populations by then. Several pointed out that kids are still vaccinated against diseases that are rare or nonexistent domestically, such as measles and polio.
Measuring efficacy
Vaccine efficacy is normally calculated in clinical trials by comparing the number of infections in study participants who got the shot to those who received a placebo. Trials are designed so that data is analyzed at predetermined points; they can be stopped if the case counts indicate no benefit from a shot, or continued to more precisely determine how well a vaccine works.
But because kids are less prone to symptomatic Covid-19 infection than adults, it could take much longer for a pediatric vaccine trial to meet the statistical bar FDA set for adult vaccine studies.
FDA officials are considering other approaches for measuring vaccine efficacy, including studies that monitor the kinds of antibodies vaccine recipients develop. If children who are inoculated against Covid develop the same amount of protective antibodies as adults — particularly if adults are as highly protected from disease as they have been in Covid vaccine clinical trials, which real-world data has so far borne out — scientists could consider the vaccine effective.
Measuring the level of antibodies in children who receive a vaccine is a well-established approach to demonstrating effectiveness in the pediatric age group, said Doran Fink, a pediatrician and deputy director in the Center for Biologics Evaluation and Research. If these concentrations of antibodies are comparable or higher than those measured in adults, the researchers consider the vaccine effective in children.
How Covid vaccines mix with routine childhood shots
People get most of their vaccinations during childhood, oftentimes receiving more than one shot simultaneously. FDA asked its advisory panel for thoughts on whether kids should be able to get Covid vaccines alongside routine childhood immunizations.
The CDC recently updated its vaccine guidance for teens and adults to endorse administering the Covid vaccine alongside other shots. The agency did that in part because its data shows many teens are now behind on routine shots after more than a year of pandemic restrictions, with orders for the tetanus-diphtheria-pertussis and human papillomavirus shots down about 18 percent compared to 2019.
One minor concern is whether co-administered vaccines could interact with each other in a way that leads to more severe side effects or reduced efficacy. “We need to look at if there’s any interference, not only with safety … and with the immune response,” said Gans.