Kids under five years old have just become the last age group made eligible for a COVID vaccine in the U.S.

A Food and Drug Administration advisory committee voted 21 to 0 in favor of authorizing the Pfizer-BioNTech vaccine for children aged six months through four years and authorizing the Moderna vaccine for those aged six months through five years. The FDA’s Vaccines and Related Biological Products Advisory Committee’s decision reflects a consensus among the panel’s health experts that the vaccines’ benefits outweigh the risks for the littlest children.

The FDA had concluded, based on its own analyses, that both Moderna’s and Pfizer’s vaccines were safe for these age groups and met its criteria for efficacy based on their immune response. If the agency follows the advisory committee’s recommendations, as it usually does, and the U.S. Centers for Disease Control and Prevention recommends the shots, they could be available to these kids soon afterward.

“For parents who want to know that they have another way to protect their child, this was a landmark day,” says FDA vaccine advisory committee member Paul Offit, who is director of the Vaccine Education Center and an attending physician at the division of infectious diseases at Children’s Hospital of Philadelphia. He likens the young children’s wait for the vaccine to a scene from the movie Jaws, in which a character describes a group of Navy sailors being stranded in shark-infested waters and waiting to be rescued by a helicopter. “The hardest time was, when the helicopters were there saving people, waiting for your turn,” Offit says, paraphrasing the line.

“As pediatricians, being able to offer this lifesaving innovation to our patients has been top of mind,” says Sallie Permar, chair of pediatrics at Weill Cornell Medicine and pediatrician-in-chief at New York–Presbyterian Komansky Children’s Hospital. “Not only are you protecting against the rare chance that your child would have severe disease, you’re also helping them achieve the normality in life that we’ve all been seeking—to keep all your current activities ongoing without interruptions.”

To many parents, the news came as a welcome relief. “I have been waiting for years for this day to come and am so grateful to everyone who worked tirelessly to make the world a bit more safe for these kids,” says Maegan Morris, a parent of a two-year-old boy in Brooklyn, N.Y. She knows the vaccines are unlikely to entirely prevent her son from potentially getting COVID, but “it’s going to give him some level of protection and will hopefully let him start to live the childhood I had hoped for him.”

The first COVID vaccines were granted emergency use authorization (EUA) for adults in December 2020, and the EUA for Pfizer’s vaccine was later amended to include age 16 and up. Pfizer’s vaccine was made available to 12- to 15-year-olds in May 2021 and to five- to 11-year-olds last October. The youngest children have had to wait the longest.

Although COVID is less likely to cause severe disease in kids than it is in adults, the fact remains that, as of June 2, 442 children younger than five have died of the disease in the U.S. (By comparison, influenza killed 87 children in this age group in the 2019–2020 season.) And many more children have been hospitalized with COVID, especially during the recent Omicron surge. Kids can develop a condition known as multisystem inflammatory syndrome in children (MIS-C), which causes inflammation in organs, including the heart, lungs, kidneys and brain. And like adults, children can suffer from long COVID.

Testing a new vaccine in children is always challenging: the requisite safety threshold is higher in a population of individuals who are still developing and are generally healthy. Additionally, older adults face the greatest risk of severe disease and death from COVID. So when the vaccines were developed, it made sense to start testing them in the latter age group first.

“We worked our way down,” Offit says. The vast majority of COVID deaths have occurred in older adults, so health experts wanted to make sure people in that age group got the vaccines first. Next they were evaluated in young adults, then five- to 11-year-olds and finally those under age five. “Parents can at least feel pretty reassured that you have billions of doses that have been out there,” he says. “So you have a lot of information, at this point, on these vaccines.”

Because young kids have a relatively low risk of getting severely ill from COVID, manufacturers and regulators wanted to be sure the vaccine did not cause side effects that were more dangerous than the disease itself. For children younger than age five, Pfizer initially tested two child-specific doses of its vaccine, each one tenth of an adult dose—but this did not produce a strong enough immune response, so a third dose was added. Moderna tested two doses of its vaccine in children younger than age six, each a quarter of an adult dose.


Children in both the Pfizer and Moderna vaccine trials experienced mild to moderate side effects—most commonly pain and redness at the injection site, headache, fatigue, irritability and fever. All were milder and less frequent than those of older children and adults except for fever, which is especially a concern in babies because it can trigger seizure. A very small number of the trial participants did have a seizure or other adverse event, but most of these were deemed unrelated to the vaccine.

There were no cases of myocarditis or pericarditis (inflammation of the heart muscle or its lining) among children six months through four or five years old in either respective trial. Rare instances of vaccine-induced myocarditis or pericarditis have occurred in older adolescents and young adults, primarily male individuals, but these cases were generally self-resolving. COVID and other infections can also cause such inflammation, and it is usually more severe than that linked to vaccines. There were no deaths among children in the trials.


The Pfizer and Moderna vaccines both produced immune responses that met the FDA’s criteria for authorization in young kids. Their efficacy was assessed by so-called immunobridging—essentially comparing the levels of vaccine-elicited antibodies that neutralize the virus that causes COVID in the youngest children against the levels in young adults.

In a preliminary analysis among children under age five, three doses of the Pfizer vaccine had an apparent efficacy of 80.4 percent at preventing confirmed COVID (75.6 percent in six- to 23-month-olds and 82.4 percent in two- to four-year-olds). Moderna’s two-dose vaccine had an apparent efficacy of 50.6 percent in children aged six through 23 months and 36.8 percent among those aged two through five years. Many of the FDA advisory committee members noted during the meeting Wednesday that the number of children in the trials were too small to draw firm conclusions about these efficacy rates, however.

Although these efficacy rates are lower than those seen in older kids and adults, it should be noted that the vaccine trials among young children took place when the relatively recent Omicron variant—which is known to partially evade immunity from vaccination or previous infection—was already circulating.

“A big difference here is that the virus changed,” Permar says. “The virus that’s circulating now is the Omicron variant, which we know to be more transmissible than any of the other variants and able to evade vaccine immunity that’s elicited by the original-strain vaccine.” The efficacy of the vaccines in young kids is in line with real-world data for adults with the Omicron variant, she says. “It’s kind of like the game changed when the trials were done for the youngest children,” she adds.

Kawsar Talaat, an associate professor of international health at the Johns Hopkins Bloomberg School of Public Health and an investigator in a study of the Pfizer vaccine in children, agrees. “It is probably unfair to compare … this vaccine as tested in small children during the period of Omicron with the same vaccine tested in adults,” she says.

The vaccines continue to provide good protection against severe disease, hospitalization and death in adults, and they are expected to provide similar protection in children.

For young kids, there are now two vaccines available with very similar mechanisms but different doses, dosing intervals and efficacies. Talaat says she is curious to see if the CDC will recommend one vaccine over the other. “I would rather have my kids have one that’s more effective, even if it takes longer,” she says, but this is “a discussion people have to have with their pediatricians, if we have the fortune of having a choice.”

Relief and Frustration

Many parents are extremely eager to get their infants and young children vaccinated. The overwhelming emotion among many of those Scientific American spoke with was relief—followed by frustration that authorization has taken this long.

Fred Blau of Brooklyn has a five-year-old daughter and a three-year-old son. He and his wife “are both very provaccination,” he says. “We were hopeful we would get our kids vaccinated in the fall or winter of 2021 or maybe in January” of this year, but “we were waiting and waiting and waiting.” Even though his son has had COVID, Blau still sees value in getting him vaccinated. “Although young children tend to have the least severe disease, there are still risks, and we would like to mitigate them as much as possible and feel comfortable getting back to our normal lives as much as possible,” Blau says.

Sarah Trist of Albany, Calif., has a 22-month-old daughter and a five-year-old son. She works at the City of Oakland’s Head Start program, a child education program for young kids, and she has seen firsthand how COVID can rip through a daycare center. “I’m waiting every day for that call from daycare that my child is quarantined,” she says. When the vaccines first came out, she was very hopeful, “but the finish line just kept moving,” with one delay after another. Now that the day is finally here, it feels “really bittersweet,” Trist says.

“The main feeling is relief,” says Allison Moy, the parent of a 20-month-old boy in Pittsburgh. “Once vaccines came out for adults and older kids, a lot of people kind of went back to life as normal,” adds Moy, who works as a microbiologist. “But that wasn’t an option for us because we had our kid to think of.” When her son’s pediatrician e-mailed parents to let them schedule vaccine appointments ahead of the authorization announcement, Moy called and booked one right away. When staff offered a choice between Pfizer or Moderna, she told them, “I don’t care!”

Not all parents are as enthusiastic, however. Fewer than 60 percent of U.S. children and adolescents age 12 through 17 have been fully vaccinated, and fewer than a third of five- to 11-year-olds have been. In a Kaiser Family Foundation poll, only about one in five parents of children under age five said they are eager to get their child vaccinated “right away,” and another two in five said they want to “wait and see” how the vaccine works. Nearly 30 percent of parents with kids that age said they would “definitely not” get their child vaccinated at all.

“As long as people don’t perceive this to be a significant infection in children, especially young children, they are unlikely to get their child vaccinated,” Talaat says. Permar agrees: “Inadvertently, leaving youngest kids to last in the trials has indicated to parents that it’s not that needed,” she says. Scientists need to rethink how they conduct clinical trials in children, Permar adds. While it’s important to do the first studies of new medical products in consenting adults, young children need to be included earlier in the process, she says.

For parents like Trist, though, the data on vaccine safety are enough. Any risk from the vaccine “is lower than the risk of COVID,” she says, and “that’s a very clear choice to make.”