Researchers need to take extra precautions when testing vaccines in children. Here’s why

There isn’t currently a COVID-19 vaccine approved for use in children under the age of 12. But it’s not uncommon in research to hold off on testing in children, for both ethical and biological reasons, according to Emmanuel “Chip” Walter, professor in the department of pediatrics at Duke University and chief medical officer of the Duke Human Vaccine Institute.

Walter said children are considered a “vulnerable population” when doing research because they can’t give consent for themselves; parents must give permission for them to be involved in trials, so researchers take “some extra precautions and protections, at least in terms of ethically, for doing research in kids.”

“Typically, you want to make sure first that when you’re giving a drug to kids, or in this case, a vaccine, that it’s been tested in adults and seems to at least work and is safe in adults,” Walter said.

Kids also are different from adults biologically — they tend to be smaller and shorter and weigh less, which could require lowering dosages when giving them medications or vaccines.

Walter said the flu vaccine used to be given to children at a lower dose, but as the vaccine has been improved over the years, it’s now recommended that children get the same dose as adults.

The COVID-19 vaccines, particularly the mRNA ones from Pfizer and Moderna, can cause side effects such as fever, sore arms, shakiness, muscle aches, chills or a general feeling of unwellness. For children, Walter said, researchers need to consider if children will experience the same side effects as adults.

“Children are generally more likely to develop a fever when they get an infection, and when they get fevers, the temperature elevations are usually higher than those in adults,” Walter said.

Too many fevers in children can cause seizures, Walter said, and pointed out that other vaccines — such as the flu, measles, mumps and rubella vaccines _ can also cause fevers and seizures in young kids.

“So you really want to kind of gradually test a vaccine in children to make sure that you’re not causing too many side effects,” Walter said. “And in the case of COVID vaccine, what we’re really balancing is side effects versus immune response for children.”

Walter is leading a study testing COVID-19 vaccines in children under the age of 12. Phase 1 of the study looked at three different dosage levels in order to fix the appropriate doses for a larger-scale pediatric trial, a process that has taken several months.

“When you think about it, because you’re testing the vaccine with increasing doses, and then you’re going down in age, it took about a month to really recruit all those kids, and then you have to follow them out through two doses of vaccine and check their titers,” Walter said.

A titer is a measurement of antibodies in a person’s blood.

The researchers are now working on expanding the study to Phases 2 and 3 where they’re now enrolling more children. Walter said that they’ve enrolled children ages five to 11 and are now continuing to enroll kids from six months up to five.

Walter would not guess when a vaccine for children under 12 would be approved and said it might vary by ages within that group.