'Children are not little adults.' Why FDA needs time to evaluate kids' COVID-19 vaccines

Millions of parents are eagerly awaiting the arrival of COVID-19 vaccines for children in elementary school. Right now, only children 12 and older may get the Pfizer-BioNTech vaccine. The Moderna and Johnson & Johnson vaccines are available only for people 18 and older.

On Friday, USA TODAY spoke with the Food and Drug Administration's Dr. Peter Marks about what the agency needs from vaccine manufacturers to authorize shots for kids and why the process takes time. Marks directs the FDA's Center for Biologics Evaluation and Research and has played a key role in nearly every major vaccine-related decision since the country's coronavirus outbreak began. 

Why aren't COVID-19 vaccines available yet for kids under 12?

"It's pretty simple. One has to actually have data that shows that they're safe and that they have evidence that they'll be effective in that population.

"I'm an adult internist and hematologist/oncologist by training, but I have had to care for pediatric transplant patients on occasion. If there's one thing that the pediatricians banged into my head, it’s that children are not little adults."

What is the FDA requiring from COVID-19 vaccine manufacturers?

"We're not expecting full-scale efficacy trials in children, but we are expecting a demonstration that the immune response that's generated in children is comparable to the types of immune responses that we've been seeing in adults. … One of the ways we can tell that people are going to be able to fight off COVID-19 is that they've developed a sufficient number of antibodies, which are proteins that are able to bind to and lead the body to clear the virus. If you make enough of those antibodies, you're protected against COVID-19. That's what we're looking at in the children."

Behind the historic US vaccine effort is FDA's Peter Marks. The job is 'not for the faint of heart.'

Why do vaccines for children have to be different from those for adults?

"They are children, with a different metabolism and their immune status is somewhat different. You have to get it right.

"Is the volume of vaccine an issue with kids? Will they get less vaccine than adults? The Moderna vaccine is a tenth of a teaspoon, and the Pfizer-BioNTech vaccine is just 6% of a teaspoon.

"We want to make sure that the dose is correct because we don't want to overdose smaller children in the 5 to 11 age range, because we're pretty sure that the adult dose is not correct there.

"One couldn't just simply take the existing formulation and just use it, because the doses are getting too small to give. … When one tries to use very small amounts of any vaccine, one runs the risk of missing some of the dose. So one usually likes to have at least a reasonable volume to administer."

When can we expect COVID-19 vaccines for kids ages 5-11?

"Pfizer actually has made public that they intend to submit data to the FDA before the end of September."

Once a company submits its information, how quickly can the FDA act to authorize the vaccine?

"There's such a desire to see the elementary school-age children vaccinated that we clearly see how important a priority that is. … If there are no surprises, I hope to see an emergency use authorization in the not too distant future after they submit those data. So a matter of weeks, not months.

"FDA is committed to going through those as quickly as we. … There’s a team of individuals who have been thinking about this and working on this tirelessly over the past months.

"There are project managers who are constantly checking their inboxes for this data. … These data will not lay around data when they come in. They’ll be looked at if not within hours, certainly within the day after they are they come into the agency."

Is there concern children might have different side effects than adults?

"We don't have any reason to think that there will be some new set of sort of side effects that will come out. If you have a safety data set of 1,000 or 1,500 children, you can rule out certain serious side effects with 95% confidence and that that is reassuring.

"We want to make sure that we're actually catching anything that could be novel in that age range population. We know from the 12- to 15-year-olds we didn't see anything new that we hadn't seen in the older age group. But children do get multisystem inflammatory disorder due to COVID-19, and that's not seen in older adults. It's pretty rare. So there are things that could be different in children, we do have to keep our eyes open to make sure there's nothing there.

"What we'd be expecting is the risk from the vaccine is very, very small compared to the benefit of protecting against COVID-19. … We've had several hundred children die in the United States (from COVID-19). No parents should lose a child to an infectious disease that can be prevented by a vaccine."

Why should parents not get their younger kids vaccinated now, before it's been studied and approved?

"As much as I think there may be some temptation, and everyone wants to do the best by their child, the right thing here is to allow us to take time. … We have to make sure that when we do it, we do it with confidence that we're not harming them in any way."

What can parents do in the meantime to protect their children?

"If you want to do the right thing right now by your children, you will get vaccinated yourself. You'll tell everyone who might come into contact with them to get vaccinated and you'll wear a mask. … We'll do our part by moving as rapidly as we can within the constraints of doing the good science that we need to do to make sure that when these vaccines are available, people will be able to be absolutely confident in their use."

Peter Marks is director of the Food and Drug Administration's Center for Biologics Evaluation and Research.