A guide to COVID-19 vaccines for the youngest kids
Children under 5, including those as young as 6 months of age, are now able to be vaccinated against COVID-19 — a year and a half after vaccines were first authorized for adults.
After more than a year of waiting, the last segment of the U.S. population without an authorized COVID-19 vaccine now has two vaccine options: one from Pfizer/BioNTech, for kids 6 months through 4 years of age, and another from Moderna, for kids 6 months through 5 years of age.
Both vaccines are messenger RNA, or mRNA, vaccines. These work by providing cells the instructions to make the spike protein of SARS-CoV-2, the virus that causes COVID-19, which the immune system responds to by generating protective antibodies and activating T cells. But the little kid versions contain less mRNA than those for older kids and adults.
The Food and Drug Administration granted the two pediatric vaccines emergency use authorization, or EUA, on June 17, after concluding that based on the collective evidence to date, the known and potential benefits outweigh the known and potential risks. An independent panel of experts advising the agency agreed in unanimous 21-to-0 votes backing both vaccines.
An outside group of experts advising the Centers for Disease Control and Prevention then recommended the vaccines for young children on June 18. The agency endorsed that decision the same day, allowing young children to be immunized starting on June 21.
When it made a decision on Moderna’s shot for little kids, the FDA also granted an EUA to the company’s vaccine for kids 6 to 11 years old and for the adult version to be given to kids 12 and over. Previously, the only vaccine available to Americans below the age of 18 for the primary series, or initial set of shots, was the Pfizer/BioNTech vaccine, including the company’s vaccine for 5- to 11-year-olds.
How are the vaccines for the youngest kids different from the older kid and adult versions?
The littlest kid vaccines are essentially identical to their older counterparts, except for the amount of mRNA, which is the “active ingredient” in the shots that the immune system recognizes and responds to, generating immunity.
The Pfizer/BioNTech vaccine for young children contains 3 micrograms of mRNA, which is a tenth of the adult dose and about a third of the dose for kids 5 to 11 years old. The Moderna vaccine includes 25 micrograms of mRNA, which is a quarter of the adult dose and half of the older kid dose.
These doses were selected in dose-finding studies, in which the companies tested different doses sequentially in a small group of children to select the amount of mRNA that elicited the most robust antibody immune response while limiting the expected side effects.
The other big difference for the Pfizer/BioNTech vaccine for little children is that the primary series includes three doses instead of two. Children should get the second dose three to eight weeks after the first, and get the third dose at least eight weeks after the second.
The dose number and schedule for the little kid Moderna vaccine is the same as for other age groups: two doses, given four to eight weeks apart.
Unlike with all other ages, boosters are not authorized for children under 5. Immunocompromised kids 6 months up to 6 years, however, are authorized to get an additional shot of the Moderna vaccine as part of their primary series.
How effective are the vaccines?
Both vaccines are expected to primarily protect young children from getting seriously ill with COVID-19, similar to how the adult and older kid vaccines have been faring against the omicron variant. The shots are also likely to provide some limited and temporary protection against infection and milder illness, and may reduce your child’s symptoms if infected.
As with Pfizer/BioNTech’s COVID-19 vaccine for older kids, the primary way the two vaccines for younger kids were evaluated for effectiveness was by comparing the antibody immune responses of children who had been vaccinated with those of young adults who had received the adult dose, and for whom clinical trials already established efficacy. In this so-called immunobridging approach, if the neutralizing antibody levels against the virus are similar, and a similar proportion of children mount an antibody response, then it is inferred that the vaccine works in younger children.
The Pfizer/BioNTech and Moderna vaccines, both of which were tested in two age subgroups, were shown to be effective using this method.
The Pfizer/BioNTech vaccine, which originally had been intended as a two-dose vaccine, did not meet this benchmark for both of its age subgroups after just two doses, which is what prompted the company to add a third primary dose to its trials and wait for the three-dose data for FDA authorization.
The companies also reported traditional efficacy numbers for preventing symptomatic disease from their randomized controlled trials. These are based on the number of kids who got placebo and fell ill and tested positive for COVID-19 and the number of children who did the same but had gotten vaccinated.
The efficacy figures, which generally tell you how much less likely you are to develop symptomatic illness if you get vaccinated, were above 90% in the adult trials — but are significantly lower and more uncertain in these pediatric trials. (As we’ll explain, this is expected and doesn’t mean the vaccines don’t work.)
For babies and young toddlers 6 months up to 2 years, the Moderna vaccine had a 50.6% efficacy against symptomatic disease (using the CDC’s COVID-19 case definition), which was based on 51 COVID-19 cases among 1,511 vaccinated babies and toddlers versus 34 COVID-19 cases among 513 placebo recipients. For kids 2 through 5 years, the Moderna vaccine had an efficacy of 36.8%, which was based on 119 COVID-19 cases among 2,594 vaccinated kids versus 61 COVID-19 cases among 858 placebo recipients.
The Pfizer/BioNTech vaccine’s figures are higher — 75.6% for babies and young toddlers and 82.4% for 2- to 4-year-olds. But those numbers are very uncertain, with massive confidence intervals stretching below zero to 98% or higher, since they included a much smaller group of kids and were based on very few sick children (three total kids in the youngest group, with one among 376 vaccinated children and two among 179 placebo kids; and seven total in the older group, with two among 589 vaccinated children and five out of 271 placebo kids).
The confidence interval in this case means researchers are 95% confident that the efficacy falls somewhere in that below zero to 98%-plus range.
Given the large confidence intervals for the Pfizer/BioNTech vaccine, Dr. Paul A. Offit, a vaccine expert and pediatrician at the Children’s Hospital of Philadelphia and a member of the FDA’s advisory committee, told us it was difficult to conclude anything about protection from these numbers. Still, he said, the antibody data was “excellent” and “enough” to know that the vaccine is likely to work.
The FDA, which chose not to report Pfizer/BioNTech’s efficacy numbers in its press release, echoed this view. Dr. Peter Marks, the director of the FDA’s vaccine division, explained in a press conference that there was less certainty with the Pfizer/BioNTech vaccine’s efficacy because it had become a three-dose vaccine, and Moderna’s two-dose data was “more mature.” But, he said, that didn’t mean the agency had concerns about the vaccine’s effectiveness, since the immunobridging data — which always was the primary criterion for authorization — looked good.
The lower efficacy figures from the little kid trials must also be understood in the context of the more transmissible and more immune-evasive omicron variant, since the pediatric trials were conducted when the omicron variant was predominant, while the adult trials were not. In other words, scientists did not expect these vaccines to post the same efficacy numbers as before, nor do they expect them to be as effective as the adult vaccines initially were for preventing symptomatic disease with earlier variants. The little kid vaccines, however, are expected to retain their ability to protect against severe illness, as has been observed with the other shots.
How safe are the vaccines?
The clinical trials for both the Pfizer/BioNTech and Moderna vaccines did not reveal any serious safety concerns. The Moderna trial included around 4,800 vaccinated children who were followed for a median of two and a half months after the second dose, while the Pfizer/BioNTech trial included about 3,000 vaccinated children, about a third of whom were followed for at least two months following the third dose.
Similar to the vaccines for older kids and adults, the most common side effects in young children were the expected, temporary effects of vaccination, including pain, redness and swelling at the injection site along with symptoms such as fatigue, headache, fever, loss of appetite or irritability. Most of these symptoms were mild and resolved within two days for the Pfizer/BioNTech vaccine or three days for the Moderna vaccine.
Such symptoms were generally more common and more severe after the second dose of the Moderna vaccine than with the first, while there was no such difference between doses for the three-dose Pfizer/BioNTech vaccine.
In the Moderna trial, about 15% to 19% of vaccine recipients developed a fever (14.6% of babies and young toddlers, 18.9% of 2- to 3-year-olds, and 16% of 3- through 5-year-olds), compared with far fewer placebo recipients (8.4% of babies and young toddlers, 10.6% of 2- to 3-year-olds, and 4.5% of 3- through 5-year-olds).
A 1-year-old girl developed a fever, rash and febrile convulsion shortly after the first Moderna dose that was possibly related to the vaccine, although her symptoms might have been caused by a viral illness, according to the FDA.
Other conditions that occurred more frequently in the vaccinated versus placebo group in the Moderna trial included lymphadenopathy, or swelling of the lymph nodes, and abdominal pain, which occurred in 0.7% of vaccine recipients 2 to 5 years old compared with 0.4% of placebo recipients. The lymphadenopathy, which affected less than 2% of children, is plausibly related to vaccination, while the FDA said there wasn’t enough information to make a determination about the abdominal pain.
In contrast to Moderna’s trial, children in the Pfizer/BioNTech trial who received vaccines were about as likely as those who received placebos to develop a fever. William Gruber, Pfizer’s senior vice president of vaccine clinical research and development, said during the FDA advisory meeting that the company opted for a very tolerable vaccine for young children because it was concerned parents would not want to give their kids shots that made them feel too crummy.
One 4-year-old who received the Pfizer/BioNTech vaccine developed a fever and pain in the calf muscle that required hospitalization. The leg pain may have been related to the vaccine, but the FDA said it could also be due to a virus.
Additionally, lymphadenopathy occurred in three Pfizer/BioNTech vaccine recipients versus zero placebo recipients.
No kids in the trials developed dangerous allergic reactions or inflammation of the heart muscle or its surrounding lining, or what is known as myocarditis and pericarditis. Those particular conditions have been rarely observed in other age groups following mRNA COVID-19 vaccination.
Offit told us that he thought it was likely that myocarditis and pericarditis would occur in some vaccinated young children, but that the risk was very low, given that the conditions have been reported after the Pfizer/BioNTech vaccine for older children, but less often than in adolescents and young adults. “
I suspect it will also be reported here,” he said, “but I suspect it’s even rarer than in 5- to 11-year-olds.”
Overall, Offit said, parents should be reassured by the safety of the two vaccines, which have become some of the most studied vaccines in history. “You have billions of people … vaccinated with these mRNA vaccines,” he said, “and for the parent of a young child, realize that millions have been vaccinated with the 5- to 11-year-old age group.”
As with all the previous vaccines, the FDA and CDC will be conducting ongoing monitoring
to identify any safety issues for young children as the vaccine is rolled out in the larger population. The two vaccine companies also are required to conduct several studies, which will include children as young as 6 months, to better understand vaccine-associated myocarditis and pericarditis.
Do experts recommend that all eligible children receive this vaccine?
Many experts and the CDC and American Academy of Pediatrics recommend that all children 6 months of age and older get vaccinated, unless they have a medical reason not to, such as an allergy to a vaccine ingredient.
Although most young children infected with the coronavirus have mild or no symptoms, some kids have been hospitalized, admitted to the intensive care unit or have died.
CDC data show that as of mid-June, around 20,000 kids 6 months to 4 years old have been hospitalized for COVID-19 since the pandemic began. Additionally, around 200 kids in that age group have died from COVID-19, a tally that accounts for 1.7% of all deaths from any cause for the age group. COVID-19 is among the top 10 causes of death for kids below the age of 1 and for kids 1 to 4 years old.
Among young children, there have been 1,990 cases of and nine deaths from multisystem inflammatory syndrome in children, or MIS-C, an inflammatory condition following infection with SARS-CoV-2 that often requires intensive care.
Studies have found young children can develop new, returning or ongoing health problems after falling ill with the coronavirus, or what’s known as “long COVID,” but it’s not known how frequently.
Serious outcomes are very rare in young kids, so it’s important not to overstate them. But as some experts and officials have pointed out, it’s exceedingly rare for young children to die from anything — and with vaccination, many of the worst outcomes are avoidable.
A CDC analysis also found that compared with other illnesses children are now routinely vaccinated for, COVID-19 causes similar or significantly more hospitalizations or deaths.
“It’s outrageous that 200 children have died — and more will — if we can prevent this,” said Dr. Sarah Long, a professor of pediatrics at Drexel University College of Medicine, during the CDC’s advisory committee meeting reviewing the data on the shots.
“Although my career in pediatric infectious diseases has been extremely long and I have saved a few lives, I have the ability with a vote today to save more lives than my particular decisions in extremely sick children have saved for my career,” she said, adding that she thinks all kids should get vaccinated.
“I think the vaccine should be available for, certainly, high-risk children” and for families worried about COVID-19, Dr. H. Cody Meissner , chief of pediatric infectious diseases at Tufts Children’s Hospital, said during the committee meeting. “But I … feel very strong that parents understand how small these numbers are. It’s a very low risk from the vaccine, but it’s also a very low risk from the infection itself.”
The committee was nevertheless in broad agreement that the benefits of the vaccines outweighed the risks and that parents should have the option to vaccinate their children.
Offit acknowledged that the risk of COVID-19 to children in the next two years is likely less than it has been over the past two, given that more of the population has some immunity.
Still, he told us, he recommended that all kids get vaccinated. Notably, only about half of young children who have had a COVID-19-associated hospitalization have had any underlying health conditions. That means, Offit said, that all children are at risk.
Everyone, he said, “has the potential of benefiting from this vaccine.”
If my child had COVID-19 already, is vaccination still recommended?
Even if a child has already had COVID-19 — which includes as many as 71% of kids 6 months to 4 years of age, according to one estimate as of this April — officials still recommend vaccination.
Immunity following infection can be variable, particularly in people who never develop symptoms or only get slightly ill, as many children may do.
“Generally, an asymptomatic or mild infection tends to induce lower levels of so-called memory cells that would be protective in the future,” Offit told us. “So I think there’s an advantage of vaccinating someone who’s been naturally infected, because you give them a known dose of what is eventually SARS-CoV-2 spike protein.”
Numerous studies have shown that a combination of infection- and vaccine-acquired immunity is likely to be superior than either alone, and could increase the durability and breadth of protection.
“There are emerging data to suggest that the omicron variant does not produce the kind of excellent immune response against a wide range of COVID-19 variants that the vaccinations do,” Marks, the FDA’s vaccine division director, said during a press conference.
If a child has recently had COVID-19, parents can choose to delay vaccination for three months after a positive test or symptom start, according to the CDC. This is because there is a low risk of reinfection during this time, although the risk could increase if a new variant emerges. At minimum, parents should wait to vaccinate until a child has recovered from the immediate illness and is no longer in isolation.
Which vaccine should my child get?
Health officials and experts advise getting the first vaccine available to your child, as there is no stated product preference. In many places, only one vaccine may be easily available to parents — and officials say it doesn’t make sense to wait to find one vaccine over the other.
“Parents should feel comfortable getting either one of these vaccines to their children,” Marks said during a press conference. “Whatever vaccine your health care provider, pediatrician, has, that’s what I would give my child.”
Still, there are differences to consider if a parent does have the option.
“It may be that the Moderna vaccine brings an immune response slightly more rapidly,” Marks said. “On the other hand, the three-dose Pfizer regimen may also bring a greater immune response after the third dose.”
And, Marks added, there were small differences in the safety profile of the vaccines, with the Moderna vaccine generally showing a higher likelihood of side effects, such as fever.
Because the two vaccines weren’t tested in parallel, it’s not possible to make direct comparisons, but in the trials, more vaccinated children in the Moderna trial had fevers than those who got placebo, whereas that was not the case in the Pfizer/BioNTech trial. Fever is an expected side effect of vaccination, and isn’t usually dangerous, but some parents might want to avoid such symptoms and opt for Pfizer.
In addition to the extra time — it would take at least 11 weeks to get all the doses of the Pfizer/BioNTech vaccine, compared with four for Moderna — another consideration for parents is whether they are likely to get all three shots of the Pfizer/BioNTech vaccine. In the FDA advisory meeting to review the vaccines, several panelists expressed concern that some children wouldn’t get the third dose, which is necessary for protection.
“The Moderna vaccine after two doses clearly induces a better immune response — and a more protective response — than does two doses of the Pfizer vaccine,” Offit told us. So dose for dose, Moderna wins out.
Offit, however, said that he thought it was likely that the Moderna regimen will ultimately include three shots as well, and that the company was expecting data on a three-dose version this summer. But for now, it’s a two-dose shot.
“The advantage of a third dose in general is that it sort of broadens protection against these current circulating strains, the omicron variants,” Offit said.
Parents should resist comparing the efficacy numbers reported in the trials. As we noted earlier, the Pfizer/BioNTech numbers are higher, but they were more uncertain than Moderna’s because they were based on so few cases — and in any event, can’t be directly compared because the trials accrued COVID-19 cases at different times, as the CDC advisory committee has explained.
Where can I get my child vaccinated?
Doses for young children are available in places such as individual doctor’s offices, community and public health centers, and pharmacies.
The CDC anticipates pediatricians in particular will vaccinate many of the youngest children against COVID-19, as these providers are among the most trusted and already immunize kids on a regular basis to protect against childhood illnesses.
Some pharmacies offer the shots, but many only vaccinate children 3 years of age and older, as not all pharmacists are comfortable with or trained to immunize very young children. (In some states, pharmacists are not normally permitted to vaccinate children of certain ages, but during a pandemic the Public Readiness and Emergency Preparedness Act allows pharmacy staff in all states to vaccinate children 3 years of age and older.)
For the rollout of these pediatric vaccines, the government updated its website, vaccines.gov, which lists nearby sites with vaccines in stock, to include information on the youngest children a particular site will vaccinate.
Should a child wait until a 5th or 6th birthday to get vaccinated with an older kid vaccine?
As we explained in our guide to the Pfizer/BioNTech vaccine for kids 5 to 11 years old, waiting leaves your child unprotected — and it’s not a given that the higher dose of the older kid vaccine is necessarily better. Multiple experts similarly told the New York Times that parents of 4-year-olds shouldn’t delay vaccination.
It’s important to remember that vaccine doses are age-based because kids and younger people have more energetic immune responses. Unlike with medications, physical size is irrelevant for vaccines — so parents of kids who are big for their age don’t need to worry that their children need to get a larger dose.
Because the two vaccine companies tested their shots in slightly different age groups, parents of 5-year-olds do have a choice between going with Moderna’s vaccine for younger kids or Pfizer/BioNTech’s vaccine for older kids.
Should little kids receive an older kid dose if they turn 5 before their second or third shot?
Yes. As with the Pfizer/BioNTech vaccine for kids 5 to 11 years old, the CDC says children should receive the appropriate vaccine based on age on the day of vaccination. That means switching to an older kid vaccine for a second or third dose if a child has a birthday between doses.
The CDC recommends, for example, that a 4-year-old turning 5 after the first or second dose of the Pfizer/BioNTech vaccine get the older kid vaccine for any dose for which the child is 5. This could mean receiving one dose of the little kid vaccine and two doses of the big kid vaccine.
However, it’s also acceptable for — and the FDA’s EUA allows — any child making an age transition between doses of the Pfizer/BioNTech vaccine to receive three little kid doses or two big kid doses. In all cases, the child would be considered to have completed the primary vaccination series. The same flexibility exists for the Moderna vaccine.
The CDC does not recommend children mix and match the Pfizer/BioNTech and Moderna vaccines during primary vaccination. If a child 6 months to 4 years of age does end up getting both vaccines, the child should receive a total of three doses.