[Originally published: June 17, 2022. Updated: Dec. 12, 2022]
After multiple delays, very young children are finally eligible for COVID-19 vaccination. In mid-June, the Food and Drug Administration (FDA) granted emergency use authorization (EUA) to Pfizer’s COVID-19 vaccine for children ages 6 months to 5 years, as well as to Moderna's vaccine for kids ages 6 months to 6 years. The Centers for Disease Control and Prevention (CDC) soon after recommended the vaccines, which should become available early next week.
While some parents have been counting down the days and are eager to vaccinate their kids, others are hesitant and have lingering questions: Are the vaccines safe? How effective are they, especially against Omicron? Should a child who recently had COVID-19 get vaccinated?
Vaccination uptake in young children has not been high to date. Nationally only about 32% of children ages 5 to 11 are fully vaccinated, according to the CDC as of Oct. 13. For ages 2 to 4, it falls to about 3% and to less than 2% for children under age 2. This compares to a vaccination rate of 60% among kids ages 12 to 17. There are roughly 18 million children under the age of 5 in the United States.
Leslie Sude, MD, a Yale Medicine pediatrician, says opening vaccination to this younger group is yet another way to manage the pandemic to make everyone safer.
“While a significant proportion of the population was not eligible for vaccination, there was still the opportunity for widespread circulation of COVID among children, who could then keep transmitting it to older people,” she says. “And as long as the virus spreads from person to person, the virus can keep changing and evolving into new variants.”
To answer parents’ questions about vaccinating young children, we talked with Dr. Sude and Thomas Murray, MD, PhD, a pediatric infectious diseases specialist.
Which COVID vaccines are now authorized for young children?
The Pfizer vaccine is authorized and approved for children ages 6 months to 5 years. (Pfizer vaccines for ages 5 and up are already available.) The Moderna vaccine is authorized for ages 6 months to 6 years.
In December, the FDA granted an EUA to Pfizer and Moderna for their bivalent booster for younger children. Shortly after, the CDC signed off on the decision.
For Pfizer, children ages 6 months through 4 years who have not started their three-dose primary series of the original, monovalent vaccine (or have not yet had the third dose) will receive the Pfizer bivalent vaccine as their third dose after completing two doses of the original vaccine. Children ages 6 months through 4 years who have already completed their three-dose primary series with the original Pfizer vaccine are not eligible for a booster dose of the bivalent vaccine at this time.
For Moderna, children ages 6 months through 5 years who received the original, monovalent Moderna vaccine as their primary series can receive a single booster of the Moderna bivalent vaccine.
In addition, a single dose of Pfizer’s bivalent booster is available to children 5 years and older at least two months after they complete either primary vaccination or receive a booster dose with any authorized or approved COVID-19 vaccine. Similarly, a single dose of Moderna’s bivalent booster is available to children 6 years and older at least two months after they complete either primary vaccination or receive a booster dose with any authorized or approved COVID-19 vaccine.
Are the COVID vaccines safe for young children?
To receive an EUA, Pfizer and Moderna separately had to present the results of clinical trials that showed their vaccines to be both safe and effective in the target age groups.
Although the results are preliminary and have not yet been peer-reviewed or published in academic journals, the data was reviewed by the FDA and a committee of independent vaccine experts. The FDA released its own analysis of the vaccines, saying they did not raise safety concerns and were effective. (Click here for an FDA analysis of Pfizer’s data analysis or here for an FDA analysis of Moderna's data.)
“There are many processes in place to ensure safety, including oversight from vaccine advisory groups, the FDA, and the vaccine manufacturers,” Dr. Sude says. “We are fortunate to live in a country that has these oversights in place. And children get smaller doses than adults do, yet they mount robust antibody responses with no safety concerns.”
Here are some more details about the safety profiles for each one:
Pfizer vaccine: Pfizer enrolled 4,500 children in its clinical trials. For those ages 5 and under, 1,678 children received two doses three weeks apart and then a third dose at least two months after the second dose. The vaccine was well tolerated and there were no new safety issues signaled; the majority of side effects were mild or moderate.
Moderna vaccine: The company enrolled approximately 11,700 children ages 6 months to 12 years in their studies, including 6,700 under 6 years old. All children received two doses of the vaccine, 28 days apart. According to data from the company, the majority of side effects (for the group under 6 years of age) were mild or moderate and mostly reported after the second dose. No new safety concerns were identified.
With both vaccines, there were no cases of myocarditis or pericarditis, conditions that involve inflammation of the heart muscle and surrounding tissue. These conditions are known, but rare, risks for young men who receive the Moderna or Pfizer COVID-19 vaccine.
Are the COVID vaccines effective?
Here are details about the efficacy of each vaccine:
Pfizer: Following a third dose, children 5 and under elicited a strong immune response, and efficacy was 80.3% in preventing symptomatic infection. These preliminary findings were based on 10 symptomatic cases identified seven days after the third dose. The immune response among children under 5 (measured one month after the third dose) compared favorably to that of two doses among 16- to 25-year-olds. It’s important to note that parts of the studies took place before the Omicron variant was predominant.
Moderna: Interim results show that the vaccine was 51% effective against symptomatic infection among children ages 6 months to 2 years, and 37% effective among those 2 to 5 years. In both age groups, two doses compared favorably to the immune response adults ages 18 to 25 had after two doses. The studies were conducted during the Omicron wave.
Vaccine efficacy was significantly lower for both vaccines in these age groups, compared with their efficacy in adults. (In the clinical trials used for the FDA EUAs of Pfizer’s and Moderna’s COVID-19 vaccines for adults, the efficacy was 94% and 95%, respectively.)
“It’s important to be clear about what we know about the vaccines so far, in terms of what they do and don’t do,” says Dr. Murray.
Overall, the adult vaccines had higher efficacy because they were created to match the original virus, which has mutated since then, he points out. “We know that people who are vaccinated against this disease can still become infected with new variants. However, the vaccines remain very helpful in reducing the severity of disease,” Dr. Murray says. “We know the vaccines still offer this greater protection for adults, and we expect the same with children. But we don’t know how these vaccines will perform in real life with respect to protection from being infected.”
Are the COVID vaccine doses for kids the same as they are for adults?
No. For the Pfizer vaccine, children under age 5 receive three 3-microgram doses. Children 5 to 11 receive two 10-microgram doses. Those 12 and up receive two 30-microgram doses, which is the same for adults.
For the Moderna vaccine, children under age 6 receive two 25-microgram doses, compared to two 50-microgram doses for ages 6 to 12, and two 100-microgram doses in ages 12 and up.
What if a child already had COVID-19?
By the end of February, three-quarters of children had already had COVID-19, according to a study from the CDC. With that number now higher, some parents might wonder if their children already have some immunologic protection based on infection.
“It’s the same answer as it is for adults,” Dr. Sude says. “The immunity we get from natural infection has some benefits vaccine immunity can’t provide, and the converse is also true. There is evidence that hybrid immunity, or natural infection combined with vaccination, may be the best type of immunity. But measuring hybrid immunity is complex and there is still much not known—for example, how long hybrid immunity lasts.”