Updated: October 30, 2021 11:45 AM EDT | Originally published: October 26, 2021 6:26 PM EDT

COVID-19 vaccines are already authorized for children ages 12 and older, and the shots now have the backing of U.S. Food and Drug Administration (FDA) for younger children ages 5 to 11.

On Oct. 29, the FDA authorized the COVID-19 vaccine made by Pfizer-BioNTech for the youngest eligible group yet to get immunized against the disease in the US. The decision followed the recommendation from the agency’s advisory committee, which concluded in a 17 to 0 vote, with one abstention, that the vaccine was safe and effective in younger kids. For these children, the FDA is recommending a two-dose regimen at one-third the dosage approved for adults.

The Centers for Disease Control and Prevention (CDC) will meet next week to detail which specific groups of children in that age range should get vaccinated. For example, after weighing the benefits of risks, the agency’s public health experts could recommend only children at high risk of severe COVID-19 get the shot, or some other subset of the larger group for which the FDA authorized the shot.

The FDA committee members struggled with that question as well, since the data presented by Pfizer-BioNTech included balancing the benefit of the vaccine in protecting kids from COVID-19 disease against theoretical risks of side effects, nearly all of which have been observed in older children and adults. Those complications include inflammation of the heart tissue, which is known as myocarditis and pericarditis.

The committee members also grappled with the fact that, according to data presented by CDC scientists, up to 40% of children aged 5 to 11 may have already been infected with SARS-CoV-2, and that may be an under estimate, since many younger children who are infected don’t experience symptoms and therefore never go to the doctor or get medical care. That means they might have some immunity against the virus, although it’s unclear how robust it would be. “I think it’s possible they likely only need one dose at best, which is going to be more than sufficient for them,” said Dr. Michael Kurilla, director of the division of clinical innovation at the National Institutes of Health, who abstained from the vote. Kurilla expressed concern that Pfizer-BioNTech did not provide data detailing what happens to the virus-fighting antibodies that children generate after getting vaccinated, and whether these wane as they do in adults. He also worried about vaccinating children who might have already been naturally infected and not need additional protection from a shot.

The U.S. is reviewing data on how safe and effective each of the three authorized or approved COVID-19 vaccines is for children. On Oct. 25, Moderna submitted its request to the FDA to expand its authorization to include children ages 6 to 11. That was based on data the company provided showing that the vaccine can provide strong protection against COVID-19 disease.

For today’s discussion, Pfizer-BioNTech provided data from two studies involving more than 3,100 children ages 5 to 11 who received either two doses of their vaccine or two doses of a placebo. About half were tracked for two months or more, and half for under a month. According to Pfizer-BioNTech’s studies, the two shots, each given at one-third of the dosage for adults, were 90.7% efficacious in protecting the children from getting symptoms of COVID-19. Three children who got the vaccine tested positive for COVID-19, while 16 in the placebo group tested positive seven days after their second dose.

The committee agreed that children with underlying health conditions, including obesity and chronic diseases like diabetes, would benefit from vaccination. But for otherwise healthy children, the balance wasn’t as clear—given, as Kurilla noted, the relatively high proportion of children who might already have immunity from natural infection, as well as the potential risk of myocarditis. In older adolescents and adults, the heart risk was rare but concerning, especially among young males, and the vaccine’s label currently contains a warning for this group. But it’s not clear if the same risk translates to younger children. That’s why the FDA asked Pfizer-BioNTech to provide additional data on more than 1,500 youngsters, in addition to the original 1,500 that the companies originally studied, which allowed the agency to delve more deeply into the side effects.

In its analysis, the FDA noted that people who are naturally infected with COVID-19 have a nearly 16-fold increase in the risk of myocarditis compared to those who are not infected. The scientists also weighed the risk of Multisystem Inflammatory Syndrome (MIS-C), a rare condition that causes fever, loss of blood pressure and damage to different organs including the liver. Over the past year, the CDC recorded more than 5,200 cases of MIS-C and 46 deaths, mostly in children ages 5 to 13 years.

The FDA scientists did extensive modeling to predict how the benefits and risks would play out, and found that the balance was highly dependent on how much virus is circulating. During peak infections, the benefits of protecting children from the disease outweigh the small risks of complications from the vaccine, but in one model, which assumed very low prevalence of COVID-19 in the community, the risk of myocarditis, estimated from rates occurring among older children, offset any potential benefit of the vaccine.

Still, overall the FDA concluded that the potential longer term risks of COVID-19 infection, including Long COVID, may tip the balance in favor of vaccination. “To me, the question is pretty clear. We don’t want children dying of COVID-19 even if there are far fewer children than adults affected by the disease, and we don’t want them in the ICU,” said Dr. Amanda Cohn, chief medical officer at the National Center for Immunizations and Respiratory Diseases at the CDC.

Ultimately, the FDA committee’s role is to evaluate the safety and efficacy of the vaccine for a specific age group. It’s up to the CDC to decide exactly which children in that age range should get vaccinated. That swayed most of the committee members to vote in favor, ensuring that children who need the vaccine and could benefit from it can get vaccinated if their parents so choose. “I voted ‘yes’ because I want to make sure that children who really need this vaccine—mainly Black and brown children—get the vaccine,” said Dr. James Hildreth, professor of internal medicine at Meharry Medical College. “There are lots and lots of children for whom the vaccine could be the difference between health and even life. I hope the [CDC’s committee] will prioritize the vaccine in some way to make sure that actually happens.”

Dr. Eric Rubin, editor in chief of the New England Journal of Medicine and professor of immunology at the Harvard T. H. Chan School of Public Health and Brigham and Women’s Hospital, admitted that “we decided to vote for it with a heavy conscience. I’m hoping this is the start of learning more about how to deploy this vaccine.”

Children, and especially younger children, are the last group to be vaccinated against COVID-19, following the elderly, adults and adolescents. As more people in the U.S. have been vaccinated, rates of new infections have declined, along with hospitalizations and deaths from the disease. But infections and disease are climbing among the youngest children, highlighting the need to vaccinate them quickly. Of the more than 44 million cases of COVID-19 reported since the pandemic began, nearly 9% have occurred among children aged 5 to 11 years. In August, 39% of cases among people under age 18 were in 5 to 11 year olds. Nearly 150 children in this age group have died of COVID-19.

Even more concerning, young children may be getting infected without symptoms and spreading the virus to others. Dr. Anthony Fauci, chief medical advisor to the White House and director of the National Institute of Allergy and Infectious Diseases, said at a recent briefing that “months ago, it was felt, based on the data with [the] Alpha [variant] predominantly, that children do not get infected as much. And if they do, they don’t spread the infection in the home setting. In the era of Delta, children get infected as readily as adults do, and they transmit the infection as readily as adults do.”

That means that as more adults are vaccinated, the virus is finding new hosts to infect to survive—such as young, unvaccinated kids who are serving as sources of infection to other children (as evidenced by the outbreaks among summer camps last year), as well as unvaccinated and immunocompromised adults.

“The reality is that at one point we thought if we vaccinated enough people, then the virus would go away,” said Jeannette Lee, professor of biostatistics at the University of Arkansas. “But it’s not going away, so we have to find a way to live with it. Vaccines give us a way to do that.”

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