A key meeting Wednesday could determine whether the nation's 18 million kids under the age of 5 could finally be cleared to get vaccinated against COVID.
Wednesday, a Federal Drug Administration committee is asking an independent panel of experts to debate and weigh in on whether the Moderna and Pfizer vaccines are safe and effectives for babies, toddlers and preschoolers.
This past weekend FDA scientists released their own analysis of both vaccines, saying in briefing documents posted online that the Pfizer and the Moderna shots appear to be safe and effective in young children.
After Wednesday's meeting, the full FDA is expected to make a final decision. So when could shots for tots begin? Are they safe, and what's the difference between the two vaccines?
Here's what we know so far.
Pfizer and Moderna Are Both Seeking Approval for Each of Their COVID Vaccines for Kids Under 5
The FDA's outside panel of advisers met Tuesday and will continue to meet Wednesday as they evaluate both Pfizer's and Moderna's shots for younger kids.
The group of independent experts will review the safety and efficacy data of the vaccines in an open public meeting, and make a recommendation on whether the agency should authorize the shots. The FDA is not obligated to follow the committee's recommendation, though it usually does.
Pfizer is asking the FDA to authorize a three-dose vaccine for children ages 6 months to 4 years old, while Moderna is requesting authorization for a two-dose vaccine for kids ages 6 months to 5 years old.
Pfizer's Plan for Kids Under 5:
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Currently, Pfizer's COVID vaccine has been the only one approved for emergency use in the U.S. for children between the ages of 5 and 17.
Pfizer's COVID vaccine for 5 to 11-year-olds contain a third of the dose given to teens and adults.
For kids younger than 5, Pfizer and its partner BioNTech lowered the dose even more, to a tenth of the adult dose. The trade-off is a need for three shots -- the first two given three weeks apart, and the last at least two months later.
The three-shot series appeared 80 percent effective in preventing symptomatic COVID, although that calculation was based on just 10 cases diagnosed among study participants.
Moderna's Plan for Kids under 6
Moderna is seeking FDA clearance for two shots, each a quarter of its adult dose, given about four weeks apart for kids younger than 6. (Moderna tested a slightly different age limit than Pfizer.)
Moderna’s two-dose series was only about 40 percent to 50 percent effective at preventing milder infections, though the two companies’ shots were tested at different times during the pandemic, when different variants were circulating. Moderna has also begun testing a booster for tots.
The FDA currently allows Moderna’s vaccine to be used only in adults. However, during a meeting on Tuesday, FDA outside experts voted unanimously that Moderna's vaccine is safe and effective enough to give kids ages 6 to 17. However, the Centers for Disease and Control would still need to review that vaccine before recommending it.
What Still Needs to Happen?
The FDA's Vaccines and Related Biological Products Advisory Committe will debate Wednesday the evidence with its scientific advisers before making a decision.
If the committee clears vaccinations for the littlest, the full FDA is expected to authorize the shots soon after.
The Centers for Disease Control and Prevention would then have to recommend who needs them -- all tots, or just those at higher risk from COVID. A CDC advisory committee is expected to meet Friday and Saturday to discuss that.
If all goes as hoped, CDC Director Dr. Rochelle Walensky will sign off on the authorization, sometimes within hours of the committee's clearance
How Soon Could Shots Begin?
Chicago Department of Public Health Commissioner Dr. Allison Arwady said she expects the FDA could could clear the way for shots to begin this summer.
"My guess right now is it will be June when we will have potentially vaccine available for those youngest children," she said during a Facebook Live. "But it all depends on the FDA and the CDC and its external experts advising."
The Biden administration said last week that children under 5 may be able to get their first COVID vaccination doses as soon as June 21, if federal regulators authorize shots for the age group, as expected.
White House COVID coordinator Ashish Jha said shipments to doctors' offices and pediatric care facilities would begin soon after FDA authorization, with the first shots possible the following week.
Jha said states can begin placing orders for pediatric vaccines on Friday, and said the administration has an initial supply of 10 million doses available. He said it may take a few days for the vaccines to arrive across the country and vaccine appointments to be widespread.
How Effective Are the Vaccines in Children? What Does the Science Show?
Whether it’s one company’s shots or both, FDA vaccine chief Dr. Peter Marks said the agency will “move quickly without sacrificing our standards” in deciding if tot-sized doses are safe and effective.
“It’s critically important that we have the proper evaluation so that parents will have trust in any vaccines that we authorize,” Marks told a Senate committee.
Earlier this year, the FDA, worried about the omicron variant's toll on kids, had taken the extraordinary step of urging Pfizer to apply for OK of the extra-low dose vaccine before it's clear if tots will need two shots or three. The agency's plan could have allowed vaccinations to begin within weeks.
But in February, the FDA reversed course and said it had become clear the agency needed to wait for data on how well a third shot works for the youngest age group. Pfizer said in a statement at the time that it expected the data by early April.
Marks said he hoped parents would understand that the agency's decision was part of its careful scientific review of the evidence Pfizer has submitted so far.
That information "made us realize that we needed to see data from a third dose from the ongoing trial in order to make a determination," Marks told reporters. “We take our responsibility for reviewing these vaccines very seriously because we’re parents as well."
In a study of kids ages 6 months through 5 years, two Moderna shots — each a quarter of the regular dose — triggered high levels of virus-fighting antibodies, the same amount proven to protect young adults, Burton said. There were no serious side effects, and the shots triggered fewer fevers than other routine vaccinations.
But the vaccine proved between about 40% and 50% effective at preventing symptomatic COVID-19 during the trial. Burton blamed the omicron variant's ability to partially evade vaccine immunity, noting that unboosted adults showed similarly less effectiveness against milder omicron infections. While no children became severely ill during the study, he said high antibody levels are a proxy for protection against more serious illness — and the company will test a child booster dose.
COVID vaccines aren't as effective against the super-contagious omicron mutant — in people of any age — and Moderna's study found the same trend.
At the same time, preliminary data suggested Pfizer and its partner BioNTech's three-dose series is 80% effective in preventing symptomatic COVID-19, the companies said, but they cautioned the calculation is based on just 10 cases diagnosed among study participants by the end of April. The study rules state that at least 21 cases are needed to formally determine effectiveness, and Pfizer promised an update as soon as more data is available.
“The study suggests that a low, 3-microgram dose of our vaccine, carefully selected based on tolerability data, provides young children with a high level of protection against the recent COVID-19 strains,” he said in a statement.
Where Would Kids Be Able to Get Vaccinated?
Pediatricians, other primary care physicians and children’s hospitals are expected to vaccinate most of the youngest kids.
Limited drugstores will offer them for at least some of the under-5 group — parents should check local availability for different ages.
The Biden administration says it also is working with a variety of other groups, such as children’s museums.
What if My Child Has Already Had COVID?
About three-quarters of children of all ages are estimated to have been infected at some point during the pandemic. It’s a question sure to come up as CDC’s advisers make recommendations for the littlest kids, so stay tuned.
For older ages, the CDC has recommended vaccination anyway to lower the chances of reinfection. There’s no firm guidance on how long to wait; the CDC has said people may wait as long as three months.
While COVID-19 generally isn’t as dangerous in youngsters as adults, some do become severely ill or even die. About 475 children younger than 5 have died from COVID-19 since the pandemic’s start, according to the CDC, and child hospitalizations soared at omicron's peak.
How Many Parents Plan to Vaccinate Their Kids?
There are roughly 18 million children younger than 5, and many parents are eager to get their tots vaccinated. But it’s unclear how many ultimately will, given disappointing vaccine uptake by older children.
According to the CDC, just 29% of kids ages 5 to 11 have gotten two doses, and about 60% of 12- to 17-year-olds.
What Side Effects Have Been Reported?
Parents may find it confusing that Moderna is seeking to vaccinate the youngest children before it's cleared to vaccinate teens. While other countries already have allowed Moderna’s shots to be used in children as young as 6, the U.S. has limited its vaccine to adults.
The FDA hasn't ruled on Moderna's earlier request to expand its shots to 12- to 17-year-olds because of concern about a very rare side effect, heart inflammation.
Heart inflammation sometimes occurs in teens and young adults, mostly males, after receiving either the Pfizer or Moderna vaccines. Moderna is getting extra scrutiny because its shots are a far higher dose than Pfizer’s.
But the CDC recently found the risk of myocarditis and other inflammatory syndromes was higher following infection from COVID than after Pfizer or Moderna vaccination in males and females ages 5 and older.
The company said that, armed with additional evidence, it is updating its FDA application for teen shots and requesting a green light for 6- to 11-year-olds, too. Dr. Stephen Hoge, Moderna’s president, said he’s optimistic the company will be able to offer its vaccine “across all age groups in the United States by the summer.”
Moderna says its original adult dose — two 100-microgram shots — is safe and effective in 12- to 17-year-olds. For elementary school-age kids, it’s using half the adult dose.
About 1.5 million adolescents have used the Moderna vaccine in other countries, “and so far we've seen very reassuring safety from that experience," Hoge said.
The heart risk also seems linked to puberty, and regulators in Canada, Europe and elsewhere recently expanded Moderna vaccinations to kids as young as 6.
“That concern has not been seen in the younger children,” said Northwestern’s Muller.
While the study wasn't large enough to detect very rare side effects, Moderna said the small doses were safe and that mild fevers, like those associated with other common pediatric vaccines, were the main reaction.
