Everything You Need to Know About the Pfizer COVID-19 Vaccine and Kids, According to an Epidemiologist

We spoke with an expert to find out what you need to know about kids’ COVID vaccines. Photograph by A. Martin UW Photography/Getty Images

As early as this week, the FDA is expected to authorize Pfizer’s COVID-19 vaccine for emergency-use authorization in adolescents ages 12 to 15, and on Wednesday, the CDC’s Advisory Committee on Immunization Practices (ACIP) will take a final vote.

“Vaccines continue to be an important public health measure in fighting the COVID-19 pandemic. To date, the FDA has authorized three COVID-19 vaccines for emergency use that have met our rigorous standards for quality, safety, and effectiveness – two are authorized for individuals 18 and older, and one is authorized for individuals 16 and older,” said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, in a statement. “We recognize that the next critical step is having vaccines available for use throughout the pediatric population.”

This comes a little over a month after Pfizer released results from its completed Phase III clinical trial, noting that its vaccine demonstrated 100 percent efficacy against the virus and produced a higher antibody response in the 12 to 15 year olds than in 16 to 25 year olds from an earlier analysis. Additionally, the findings showed that participants experienced similar side effects as 16 to 25 year olds, including soreness at the injection site, low-grade fever, body aches, and fatigue.

Given that parents and guardians could soon have the option to take their dependents to get vaccinated, we spoke with Stanley Weiss, epidemiologist in infectious and chronic diseases and professor at the Rutgers New Jersey Medical School and the Rutgers School of Public Health. Below, he offers insight into all the things parents and guardians might be wondering right now about vaccines and kids — the benefits, trial and approval considerations, and potential expansion to even younger age groups.

A main question I’ve seen circulating regarding this topic is, “Is vaccinating my kid necessary?” Is it?
Weiss: Yes, vaccinating the youth is necessary for several reasons. First, we have to keep in mind the benefits of vaccination: protection of the individual and the community. For a long time, we weren’t too worried about children getting ill [with COVID-19], but that has changed within recent months. We’ve now recognized that even persons who are asymptomatic are still at risk for long-term complications. These “long-haulers” are more common among youth than we had originally suspected. Additionally, these new variants that are arising and rapidly taking over in parts of the world seem to more efficiently infect kids than the original strain. This creates an ongoing and future danger, especially if someone is not vaccinated.

Also, as schools continue to open, we have to remember that kids have more chances for infection acquisition and transmission: the cafeteria, gym, sports, and such. The CDC has reported outbreaks in schools that have occurred when prevention strategies were not in place, leading to transmission among students, teachers, and staff.

How might the eligibility expansion benefit other areas of kids’ lives?
Everyone wants to see society return to a state of normalcy. For that to happen, we have to have a very high fraction of the population vaccinated. This includes youth, particularly because of the increased concern regarding transmission among and due to this age group. If kids are vaccinated, they can start to have a more normal social experience again. We know that the socializing aspects of school and life in general are extremely important to their development — and remote virtual learning hinders that a bit.

Getting kids vaccinated might also allow them to forgo a mask. This is huge because finding a well-fitted mask for kids can be tough in general. Plus, even after you find one for them, kids typically run around and play a lot more than adults, which can cause the mask to come loose. When engaged in vigorous sport, it’s often not practical to wear a mask. And yet, they currently have to, due to the increased contact and breathing, both of which contribute to the spread of infection. Overall, vaccinating kids is both a protective measure for them and others, and a means to help them achieve a much more “normal” life.

How is approving vaccines for use in youth different than for use in adults?
If a trial participant is younger than 18 years old, then a two-fold consent must occur: parental/guardian consent and the minor’s own. Additionally, sometimes clinical trials (and therefore approval) take longer when a protected or special population (i.e. children and pregnant women) are involved. Those two groups are typically excluded from initial trials because there are more variables that need to be taken into account.

Also, researchers leading trials on youth still have to determine what dose is going to be given. Just because adults are receiving two doses [of Pfizer] does not mean kids will receive the same. Also, those dosing regimens might be altered within that age range — a six year old might not end up receiving the same dose as a sixteen year old. So, just like researchers did in the trials involving adults, a range of doses will be examined and an appropriate dose for each age group will be selected from that data.

Another issue to consider for approval is needle size. The CDC has general guidance on needle gauge and length, but I have yet to see guidance specific to COVID-19 vaccines. The Pfizer vaccine has been designed for intramuscular administration, which means you need a needle that safely reaches the muscle. But, on average, kids’ arms are skinnier than adults’ arms, so the needle size used on adults is obviously not going to be the one used on kids. I am not the one who can tell you what size will or should be used for youth, but I do believe that is an additional factor that will or already has been taken into consideration for impending approval.

I think the final consideration is the fact that the frequency of [other] virus exposure is typically greater among children than among adults. That means the mix of past virus antigen exposure in youth trial participants may be quite different from the adult trial participants. That could add to the length of trial and/or approval time.

How will scientists know the vaccines work and are safe for youth?
The data Pfizer released from their clinical trials shows their vaccine demonstrated 100 percent efficacy on children aged 12 to 15. The evidence from that trial also shows that that age group is not at any increased [health] risk than adults. Trial participants will continue to be monitored for long-term effectiveness and safety for an additional two years after their second dose.

Do children’s immune systems respond differently to the vaccine than adults’?
We should make the assumption that it is possible a child’s immune system will respond differently to a vaccine than an adult’s immune system. On one hand, they have a past set of exposure to other coronaviruses (like the cold) from being around a number of other children in various settings. On the other, there are age-dependent issues in the development of our immune system, which means that a child’s immune system can be both more potent for some things and less potent for others. But that’s also why you receive many vaccines when you’re a child, so that you have a better chance at fighting off antigens when you’re young. [Note: Pfizer’s early trial results have shown that 12 to 15 year olds who received two standard doses of the vaccine developed higher levels of virus-blocking antibodies than did 16 to 25 year olds.]

This impacts what I was saying earlier about dosing regimens. Maybe kids will only need one shot or they might need three shots. I’m not the one who can say what the most appropriate dose for adolescents and younger children might be, but I do think that parents and guardians should be prepared for a potential dosing difference.

Are there any potential risks to vaccinating kids?
The surveillance systems looking for even rare outcomes are identifying those. An example is the blood clots that people got so worried about [regarding Johnson & Johnson’s vaccine]. But the rate of those blood clots was extremely low, and the risk of developing blood clots is much higher if you acquire SARS-CoV-2. So really, concern over severe health complications should make someone want to get vaccinated, since they are more likely to occur with the infection than with the vaccine.

What might it take to get a vaccine approved for use in children younger than 12?
Not much will be different in terms of designing the clinical trial. It will involve performing statistical calculations of how many outcomes researchers need for analysis, analyzing the data, and looking for the evidence of protection, with the hope that any adverse effects occur in the control group because the vaccinated group performs well. I could see that population getting divided into subgroups because a six month old is not the same as an 11 year old. As long as the considerations I mentioned earlier are taken into account (previous virus exposure, dosing regimen, needle size) and trial data demonstrates efficacy and safety, then I think there’s the possibility the vaccine could be approved for this younger age group.

Do you think multiple vaccines will be available to kids this year?
Yes, I think so. Both Johnson & Johnson and Moderna are undergoing clinical trials on adolescent and pediatric participants in order to extend their age eligibility. The other companies are clearly doing the work to get their vaccines available to other age groups, which makes me believe — if their trials go well, which they should — that they will likely expand their age eligibility.

Are there any other special considerations parents or guardians should keep in mind?
Something parents and guardians will need to discuss with the pediatrician is the timing of other vaccinations their children get at various ages. They will need to plan around their child’s vaccine schedule, but I’m sure the CDC will come out with guidance surrounding this. [Note: Currently, the CDC recommends that the COVID-19 vaccine series be given alone, with a minimum interval of 14 days before or after administration of any other vaccine, except for situations in which the immediate benefits of vaccination might outweigh the potential unknown risks of coadministration.]