Testing COVID-19 vaccines in young children is going to be tricky. Deciding how to approve them and who should get them may be even more difficult.
So far, the vaccines available to Americans ages 12 and up have sailed through the U.S. Food and Drug Administration’s regulatory checks, taking advantage of an accelerated clearance process called an Emergency Use Authorization (EUA).
EUAs set a lower bar for effectiveness, saying the vaccines may be safe and effective based on just a few months of data.
But with COVID cases plummeting in the United States and children historically seeing far less serious disease than adults, a panel of expert advisors to the FDA was asked to deliberate on Thursday whether the agency could consider vaccines for this age group under the same standard.
Stated another way: Is COVID an emergency for kids?
There’s another wrinkle in the mix, too – heart inflammation, which appears to be a very rare emerging adverse event tied to vaccination. It seems to happen more often in teens and young adults. To date, cases of myocarditis and pericarditis appear to be happening in 16 to 30 people for every 1 million doses given.
But if it is conclusively linked to the shots, some wonder whether it might tip the balance between benefits and risks for kids.
That left some of the experts who sit on the FDA’s advisory committee for vaccines and related biological products urging the FDA to take its time and more thoroughly study the shots before they’re given to millions of children.
Vaccine studies different in children?
Clinical studies of the vaccines in teens and adults have thus far relied on some straightforward math. You take two groups of similar people. You give half the vaccine and half a placebo. Then you wait and see which group has more symptomatic infections. To date, the vaccines have dramatically cut the risk of getting severely ill with COVID for every age group tested.
But COVID infections are falling rapidly in the U.S., and that may make it more difficult for researchers to conduct a similar kind of experiment in children.
The FDA is considering different approaches to figure out whether a vaccine would be effective in kids, including something called an “immunobridging trial.”
In bridging trials, researchers don’t look for infections; rather, they look for proven signs that someone has developed immunity, like antibody levels. Those biomarkers are then compared to the immune responses of younger adults who have demonstrated good protection against infection.
The main advantage of bridging studies is speed. It’s possible to get a snapshot of how the immune system responds to a vaccine within weeks of the final dose.
The drawback is that researchers don’t know exactly what to look for to judge how well the shots are generating protection.
That’s made even more difficult because kids’ immune systems are still developing, so it may be tough to draw direct parallels to adults.
“We don’t know what the serologic correlate of immunity is now. We don’t know how much antibody you have to get in order to be protected. We don’t know what the role of T cells will be,” said H. Cody Meissner, MD, chief of the division of pediatric infectious disease at Tufts Medical Center, Boston.
“I have so much sympathy for the FDA because these are enormous problems, and you have to make a decision,” said Dr. Meissner, who is a member of the FDA’s vaccines and related biological products advisory committee.