FDA authorizes COVID-19 vaccines for children under 5 years old. What's next?

Editor's note: This article's headline has been updated.

The U.S. Food and Drug Administration's vaccine advisers gave the green light to Moderna and Pfizer to administer their COVID-19 vaccines to children under 5 years old—roughly 18 million American kids. The benefits of vaccination for this group, the panel agreed, far outweigh the risks.

If the remaining regulatory procedures go as planned, shots could be available to this vulnerable population—the last remaining group of Americans without access to COVID-19 vaccines—as early as next week.

For insights into the issue of vaccinating our youngest kids, Joshua Sharfstein, host of the Public Health On Call podcast, spoke with Ruth Karron, a professor of international health and director of the Johns Hopkins Center for Immunization Research. She discusses why it's taken so long to authorize vaccines for young children, why vaccinating this age group is important, and what's likely to happen in the next few weeks.

Why has it taken so long to make vaccines available for young children?

There are a couple of reasons. The first is that when we started to make COVID-19 vaccines in 2020, I don't think we appreciated the full burden of COVID on young children. Certainly we appreciated the indirect effects on schooling and other social activities, but it took us a while to fully appreciate the direct medical effects.

The second piece is that we're using a new vaccine platform for COVID-19 vaccines: mRNA. It's highly effective, but it is also inflammatory. Anyone who's gotten these vaccines knows that you can have low-grade fever, chills, and aches of various kinds. And one of the things we know about children is that their inflammatory reactions are heightened. Children get fevers, for example, much more frequently than adults do.

The companies and the bodies that regulate these vaccines wanted to make sure that they were being evaluated as carefully as possible, to ensure that a vaccine would be safe to administer to children.

How did learning that children could develop Multisystem Inflammatory Syndrome, or MIS-C, after COVID-19 affect your thinking about the importance of the vaccine?

This inflammatory response in children, MIS-C, is severe and quite frightening. We don't fully understand it, even now. It happens not during the acute infection but shortly thereafter. And it certainly made many people think that it might be important to develop a vaccine early on. Because this was understood to be an abnormal immune response to the virus, people wanted reassurance that vaccination wouldn't make it worse.

One of the important things we've learned as we've used vaccines in adolescents and children over age 5 is that it decreases the rate of MIS-C. It doesn't exacerbate it.

That's reassuring, but for me personally, the case for vaccinating children against COVID became clear in the late summer and early fall of 2021 with delta. By the time we got to omicron and child hospitalizations were surging, the case became very clear.

Why do you think kids should be vaccinated against COVID?

This virus is smarter than we ever imagined. I remember saying in 2020 that this virus has got it made because it transmits really well. That was true of the early isolates of SARS-CoV-2. Omicron and its subvariants are more transmissible than measles—one of the most infectious diseases we know of.

What that means is that virtually everybody is going to get infected with this virus sooner or later. So, even if complications in children are rare, if everybody is getting infected, the absolute number of children who will have serious disease or who will die is not a small number.

Right now, the CDC estimates that 1,200 children have died of COVID. We're talking for the most part about generally healthy children or children with minor medical issues. This is a tragedy. Whatever we can do to avoid this tragedy is something we should do.

For any one child, the risks may be low, but if you look across many children, you see some pretty severe outcomes.

Exactly. While I completely agree that the nonpharmaceutical interventions like masking are important, people do need to continue to lead their lives. Children need to be in school. Children need to be playing sports and congregating. This is part of childhood. Our children have lost years to this pandemic, in a much more profound way than adults have.

A lot of parents are interested in vaccinating their young kids, but vaccines haven't been available for them.

Moderna and Pfizer have each applied to the FDA for an emergency use authorization, and the FDA is reviewing these applications and will hold public meetings with its advisory committee in June. We don't know the exact dates yet, but we're hopeful that we will have one or both of these vaccines available for use in children sometime [in June].

That's an optimistic view. There have been some challenges with these trials to date.

There have been. Many people probably know about the Pfizer trial, which was originally for most normal, healthy adults and older children. Two doses of vaccine is what we consider a primary series of vaccination, and Pfizer was understandably very cautious in its dosing of vaccines for the youngest children. The dose for children under 6 months to 4 years of age was one-tenth of the dose given to adults—3 micrograms instead of 30 micrograms.

Early this year, Pfizer discovered that while it was safe, it did not produce the same immunity that they had seen in older children and adults. They've given a third dose of vaccine to this youngest age group, and that's what they've applied for FDA authorization for. The Moderna vaccine is given as a two-dose series.

Is the FDA going to wait to review both the Pfizer and Moderna vaccines at once, or each as it's ready?

I think the agency has heard loud and clear from groups like the American Academy of Pediatrics and from parents that the time is now to consider these applications so that these youngest children can be protected. They are in the process of reviewing all of the data. There are challenges, of course, with vaccines for very young children. You absolutely want these vaccines to be as safe as possible.

The other complicated thing is that you're looking at efficacy data against a virus that's perpetually changing, so interpreting that data and the immune response is more challenging.