A Guide to Pfizer/BioNTech’s Pediatric COVID-19 Vaccine for Kids 5-11

The lower 10-microgram dose was selected in a phase 1 dose-ranging trial, in which several doses were tested sequentially in a small group of children, with the kids being monitored for side effects and their immune responses evaluated by measuring how many coronavirus-specific neutralizing antibodies they produced. 

Because the lowest dose of 10 micrograms provided a similar immune response to a 20 microgram dose but was accompanied by fewer side effects, it was chosen to be tested in the subsequent phase 2/3 clinical trial.

Another difference between the two vaccine formulations is in the buffer, or solution that helps the vaccine maintain proper pH. Thus far, the adult vaccine has used phosphate-buffered saline, or PBS. But Pfizer switched to using another buffer known as Tris, or tromethamine, in the kids’ version because it increases the stability of the vaccine and allows the vials to be stored at warmer temperatures for a longer period of time.

Both buffers are common in medical products, including other vaccines for children, and have been shown to be safe.

Nevertheless, the change has led some people online to falsely suggest that the children’s shot is either not safe or indicative of a problem with the vaccines.

Pfizer told FactCheck.org that the modification does not change manufacturing and that the adult formulation of its vaccine will also soon use Tris for the same stability improvement.

“The manufacturing processes involved in producing the pediatric doses remain unchanged from the adult and adolescent doses. There are also no changes in raw materials, mRNA, lipids or suppliers in the manufacturing of the drug substance and lipid nanoparticles,” the company said in an email (emphasis is Pfizer’s). “To enable extended storage time an alternative buffer is being leveraged, known as a ‘tris buffer’. Simply put, this allows the mRNA to resist being degraded for a longer period of time before administration — meaning the pediatric vaccine can be stored for 2-8°C in commonly available refrigerators for up to 10 weeks. This buffer will also be used in the updated adult/adolescent 30mcg doses in due course, helping to ensure simplified handling of the vaccine across age groups.”

The pediatric trials did not use the Tris formulation, but the FDA has said lab tests were done to ensure the change did not alter the vaccine’s safety or effectiveness, and that the switch is “not considered clinically significant.”

Dr. H. Cody Meissner, chief of pediatric infectious disease at Tufts Children’s Hospital, and a member of the committee advising the FDA, also told us that he didn’t think the change in buffers would “make much of a difference at all.”

Finally, because of their smaller size, kids are injected with slightly less fluid than adults and the needles used are also tinier. To avoid confusion for vaccine administrators, the children’s version comes in an orange vial while the adult version is in a purple or gray vial.

How effective is the vaccine?

Preliminary data from a randomized, placebo-controlled trial showed that at least a week following the second dose, two doses of the vaccine were 90.7% effective in preventing symptomatic COVID-19 in children 5 through 11 years of age. This figure means that a vaccinated child is about 90% less likely to fall ill than a similar unvaccinated child.

In the study, which is ongoing and has enrolled about 4,700 kids in the U.S., Finland, Poland and Spain, two children received the vaccine for every child receiving a saline placebo. As of Oct. 8, three COVID-19 cases occurred among 1,305 vaccinated children compared with 16 in 663 placebo recipients, which is how the 90.7% number is derived.

Symptomatic disease was defined as having at least one symptom and a positive test for SARS-CoV-2 infection. Most of the cases occurred over the summer, when the delta variant was widespread. No cases in either group were considered severe, and there were no deaths.

These data, however, are considered supplemental, and were not the primary way regulators assessed effectiveness. Instead, the plan was to take a so-called immunobridging approach, in which a random selection of children in the trial are evaluated for their immune response to the vaccine, which is then compared to that of young adults receiving the adult dose, for whom a clinical trial previously demonstrated efficacy. If the immune response is similar, or what is termed “non-inferior,” then it is inferred that the vaccine works in younger children.

In this case, scientists looked at the average SARS-CoV-2 neutralizing antibody titers one month after the second dose in 264 kids 5 through 11 years old and compared it to the average observed in 253 vaccinated 16- to 25-year-olds. Pfizer’s study found the averages to be the same (see page 22). Additionally, the same proportion of individuals in each age group — 99.2% — produced antibodies following vaccination.

It is not known how effective the vaccine is at preventing children from becoming infected or spreading the coronavirus, as that was not explicitly studied in the clinical trial. However, if the vaccine performs similarly in children as in adults, the pediatric vaccine should reduce — although not eliminate — both infection and transmission.

How safe is the vaccine?

Safety was evaluated in around 3,100 children who received the pediatric Pfizer/BioNTech vaccine, and no serious concerns were identified. About half of these children were followed for at least two months after their second dose, while the other half had a median of a little more than two weeks of safety data.

Similar to the adult vaccine, the most common side effects in children were pain, redness or swelling at the injection site, as well as fatigue, headache and muscle pain. However, these side effects were generally more mild and less frequent in children than in those receiving the adult dose. Most of these reactions were mild and resolved within one or two days and often were worse after the second dose.

Less than 1% of children developed lymphadenopathy, or swelling of the lymph nodes, and a similar number experienced a rash. The only serious adverse events observed in children, such as a broken arm, were deemed by the FDA to be unrelated to vaccination.

No kids in the trial developed dangerous allergic reactions or myocarditis or pericarditis. However, because those conditions have on rare occasions occurred in people following vaccination with Pfizer/BioNTech’s adult vaccine, regulators do expect them once the pediatric vaccine is rolled out to millions of children.

It is not yet known how common myocarditis will be in children following vaccination with the pediatric Pfizer/BioNTech vaccine. In a positive sign, vaccine-related myocarditis appears to be less common in 12- to 15-year-olds than in 16- to 29-year-olds, suggesting the risk would be even lower in younger children, especially given the lower amount of mRNA used in the vaccine. Traditional myocarditis is also less common in younger children, further lending credence to that hypothesis. But it remains an important unknown.

In its benefit-risk assessment, the FDA modeled a series of scenarios assuming the myocarditis rate in vaccinated kids 5 through 11 years old is the same as in 12- to 15-year-olds. The agency then incorporated different variables, such as different levels of protection afforded by the vaccine, along with different levels of coronavirus circulation and COVID-19 death rates in children. According to the model, the vaccine prevents more bad outcomes from COVID-19 than it causes in all scenarios, except for the one in which viral transmission falls to its low point in June. In that case, there are more hospitalizations due to vaccine-related myocarditis than those prevented from COVID-19, but because vaccine-related myocarditis is usually less serious than typical myocarditis, the FDA said the overall benefits still might outweigh the risks.

The FDA and CDC will be monitoring for any serious side effects of this vaccine in children, but are keeping an especially close eye on myocarditis.

Do experts recommend that all children receive this vaccine?

Many experts and the CDC and American Academy of Pediatrics recommend that all children 5 years of age and older get vaccinated, unless they have a contraindication, such as an allergy to a vaccine ingredient. 

While infection with the coronavirus is typically mild or without symptoms in young children, some kids have been hospitalized and have died.

According to the CDC, since the pandemic began, there have been at least 1.9 million cases of COVID-19 in U.S. kids 5 to 11 years old, including 8,300 hospitalizations and 94 deaths. The death toll, while low, is enough to have made COVID-19 one of the top 10 causes of death in 2019 among children in this age group. 

There also have been at least 2,316 cases of multisystem inflammatory syndrome in children, or MIS-C, an inflammatory condition following infection with SARS-CoV-2 that is fatal 1% to 2% of the time and requires intensive care in 60% to 70% of cases. MIS-C is rare but is most common in the 5-to-11 age group.

Additionally, a U.K. study found 7% to 8% of children experience symptoms more than 12 weeks after diagnosis, even if the initial infection is mild. This suggests children do get “long COVID,” although to a lesser degree than adults.

On the other side is the potential risk of myocarditis, which most experts consider to be a real, albeit rare, side effect of the Pfizer/BioNTech vaccine.

“In my mind, it really is not a close clinical call,” said Dr. Ashish Jha, dean of the Brown University School of Public Health, in a Nov. 3 press call with reporters. “I think every child in America 5 to 11 should get vaccinated.”

Dr. Paul A. Offit, a vaccine expert and pediatrician at the Children’s Hospital of Philadelphia who is also on the FDA’s advisory committee, agrees.

“It should be all children who are 5 to 11,” he said in a phone interview.

At the FDA advisory committee meeting, however, some members expressed reservations about rolling out the vaccine to all children and especially of mandating it, when the risk of COVID-19 is so low to young children and the myocarditis risk of the vaccine is not yet fully known.

Tuft’s Meissner, for example, said he was concerned about states issuing mandates for children to be vaccinated to attend school. “I think that would be an error at this time, until we get more information about the safety,” he said.

Dr. Michael Kurilla, the director of the division of clinical innovation at the National Institutes of Health’s National Center for Advancing Translational Sciences — and the sole person not to back the vaccine with a “yes” vote — was not convinced that all children would necessarily benefit all that much from the vaccine, especially when CDC data suggest around 40% of children may already have been infected.

“While there are clearly high-risk groups within the 5 – 11 age group for which this vaccine would significantly reduce serious disease, I do not expect protection from infection to last more than a few months and this may negatively impact public perception of vaccines,” he said in a statement to FactCheck.org explaining his abstention vote. “Taken together, I don’t see the need for ‘emergency use’ of this vaccine across the entire age group and would have preferred a more nuanced approach.”

Offit, however, disagrees, noting that while around two-thirds of children who were hospitalized with COVID-19 had one or more underlying risk factors, that still leaves a good chunk who were not. 

“One-third of those children who were hospitalized were perfectly healthy prior to that,” he said. “So I don’t think you can reasonably kind of layer the recommendation to include just those with certain comorbidities.”

“It should be striking to parents that this virus in terms of mortality is in the top 10 causes of death,” he said. “A choice not to get a vaccine is not a risk-free choice. It’s a choice to take a different risk.”

Other committee members were ultimately swayed by the data, but recognized the challenges of the remaining uncertainty. 

Dr. Patrick Moore of the University of Pittsburgh School of Medicine called the decision a “hard … but a clear one,” and Dr. Michael Nelson of the University of Virginia School of Medicine emphasized the need for parents to have conversations with their pediatricians.

“Providing choice to a fully risk-informed public using a shared decision-making model with their trusted providers, to me, is a pretty reasonable way ahead,” he said, adding that there were millions of high-risk children and family members who needed the vaccine.

In a phone interview, Meissner said he voted “yes” because he wanted the vaccine to be made available to anyone who wanted it, but also said that it should be made clear to parents that the myocarditis risk is not fully known and that it’s possible the vaccine could cause more hospitalizations than it prevents.

Although most of the vaccine-related myocarditis cases appear mild and self-resolving in adults, he noted that some patients still show abnormalities on MRI scans, and it’s not yet known what that means.

“Based on the facts that we have now, I think many parents may elect to wait and see what the experience turns out to be with other children in this age group,” he said, “and I think that’s a very reasonable approach.”

If there is a risk that outweighs the benefits, Meissner said, that should become clear within several months.

“I think that the United States has the best safety monitoring system in the world,” he said. “That’s why I would feel comfortable waiting a few months, until the vaccine safety signal is clear and there aren’t problems. And then, I think, it would be reasonable to go ahead with a strong endorsement for administering the vaccine.”

When and where can I get my child vaccinated?

Federal officials began shipping pediatric vaccines to providers as soon as the FDA authorized the shots on Oct. 29, but have cautioned that the program will not be at “full strength” until the week of Nov. 8. 

Some experts also suspect there may be delays past the first few days.

“My expectation is the next few weeks, it’s going to be hard to get vaccines, because there’s a lot of pent up demand,” said Brown University’s Jha. “About 30, 35% of American parents — including me — are very excited to get their kids 5-11 vaccinated. That’s, you know, probably about 9, 10 million children, and it’s going to take a while to just get all those kids there for a shot.”

In a bit of a change from the adult vaccine, more pediatric doses will be available in places such as individual doctor’s offices and community health centers, along with pharmacies and in larger-scale clinics hosted at children’s hospitals. The government has a website, vaccines.gov, that can help parents and guardians find locations giving out shots.

If my child gets vaccinated, does that mean they don’t have to wear a mask at school?

That will depend on your child’s school policy, but experts are hopeful that as more elementary school kids become fully vaccinated, some of the mitigation measures instituted to make classrooms safer can fall by the wayside.

“I believe that once vaccines are widely available over the next couple of months, being able to pull back on the mandates for masks is going to be very, very reasonable,” said Jha, adding that masks might still make sense during small outbreaks or for high-risk children.

“With large-scale vaccination of kids, we really can get back to what I think is a new normal,” he said, “where sports, activities — all the things that are so important beyond just being in the classroom — should really resume in a way that looks a lot more like 2019.”

But Jha also cautioned against removing masks too soon. “A month is not enough,” he said, since even a child who gets a shot immediately would not be considered fully vaccinated until five weeks later, two weeks after the second dose.

“I understand that some school districts may want to move quickly on this,” he said. “What I would say is, give parents time to get their kids vaccinated. And if we do that, it’s going to be much more reasonable to pull back the mask mandates down the road.”

Should nearly 12-year-olds wait until their birthday to get vaccinated so they can receive the adult vaccine series?

You should consult with your child’s pediatrician, but waiting to be vaccinated could leave a preteen susceptible to COVID-19, as Dr. Sallie Permar, the chair of pediatrics at Weill Cornell Medicine, told the Atlantic and multiple other experts told the New York Times.

There also may not even be any advantage — and your child might have an easier time with the temporary side effects with the lower dose.

“I think I would actually prefer to get them the lower dose,” Permar said. “Pediatric immune systems are more well set up to respond to low doses. They may even achieve a better response. We’ve been studying this in the HIV-vaccine world for several years now. A lower dose in a young age group can achieve a better immune response than even a higher dose.”

While these age cutoffs are arbitrary on one level, there is a solid basis for giving younger people a lower vaccine dose than older people — and it’s not because of a person’s size. The rationale has to do with the development of an individual’s immune system.

Younger people — and especially younger teens and kids — tend to have more energetic responses. Vaccine doses therefore can be lower for them, and this also helps keep the side effects more manageable. Conversely, for older people, sometimes higher-dose vaccines are needed to ensure a robust response.

There is no need to worry that your large-for-his-age 10-year-old would be less protected or need an adult dose because of his larger physical size. Unlike medications, which often need to be prescribed by weight because a compound will only work at a certain concentration, vaccines are not based on weight and do not need to be sized-up for larger bodies.

The trial data did not show differences in neutralizing antibody levels in 9- to 11-year-old children versus 5- to 6-year-old kids. Of the three cases of mild COVID-19 in the kids who were vaccinated, two were in 10-year-olds and one was in an 11-year-old. It is unclear whether that is indicative of anything, though, as this could reflect the higher exposure to the virus among older children, as older kids in the placebo group were also more likely to fall ill.

That being said, it may depend on exactly how close your 11-year-old is to turning 12. With other vaccines, there is often a four-day grace period that allows providers to inoculate children four days earlier than recommended — and the CDC has said that rule will also apply here.

Should children receive an adult dose if they turn 12 before their second shot?

According to the CDC, children should receive the appropriate vaccine based on age on the day of vaccination. That would mean if a child is 11 years old for their first dose and 12 years old three weeks later, they should receive a pediatric shot followed by an adult shot. 

But of course, nothing magical happens when a child turns 12, so the agency has also stated that if a children’s vaccine is given to a 12-year-old in this scenario, “they do not need to repeat the dose and this is not considered an error.”

The FDA has said that these kids “may receive” either a pediatric or adult shot for either of their doses, while experts with the American Academy of Pediatrics recommend sticking with the kids’ version for both doses.

Will kids need a third dose or ‘booster’?

It’s possible children will need a third dose, but at this time there is no data to suggest an extra shot is needed, nor has one been shown to be safe and effective in younger children. For this to become an option, vaccine makers would need to present data to the FDA and CDC and the regulatory agencies would have to sign off on it first.

Third shots of the mRNA vaccines are currently only available to children 12 years of age and older who are immunocompromised.

Will the COVID-19 vaccine be required for elementary school students?

It’s possible that eventually COVID-19 vaccination will become a prerequisite for enrollment in some public schools, much the way other vaccines for childhood diseases are required. 

But experts are skeptical that mandates would happen very soon — and many are opposed to them for children, at least for now.

In the FDA advisory committee’s discussion, multiple members, including Tuft’s Meissner, were particularly concerned about a “yes” vote being misinterpreted as supportive of a mandate at this time, which was not their position.

In an effort to reassure the committee, Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, pointed out that mandates are less likely when a vaccine has only emergency use authorization, and several governors have specifically stated they would not implement a mandate without full approval.

Similarly, Jha noted that COVID-19 vaccine mandates for adults did not arrive on the scene for about six months — and that he suspects any mandates for kids would also come later.

“Back in December, we did not have vaccine mandates immediately. We let people choose to get vaccinated or not,” he said. “That’s how I envision what should be happening with children right now — is let kids get vaccinated, give parents time to have those conversations with their pediatricians, let people get comfortable with this.”

Jha said that while he’s generally supportive of vaccine mandates for other people, he did not think that they are appropriate right now for 5- to 11-year-old children.

Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.