Three-Dose Pfizer Covid Vaccine Works Safely in Young Children, Review Says

The assessment is the latest sign that authorities are moving closer to clearing inoculations for children under 5 years old, the last group ineligible for Covid-19 vaccination.

On Friday, the FDA released a staff review finding that two doses of Moderna Inc.’s Covid-19 vaccine were generally safe and effective in children ages 6 months through 5 years old.

The FDA could make a decision within the next week on authorizing the two vaccines for use among young children, after vaccine experts advising the agency consider the data on the shots and make a recommendation.

Some parents have been eager to get their young children inoculated, though surveys find that other parents are hesitant or don’t want to.

The Biden administration has said vaccinations for young children could begin June 21, depending on the decisions of federal health agencies.

The FDA typically releases a review of the evidence for a medicine before deciding whether to OK it. The FDA’s new assessment of Pfizer’s vaccine will inform a meeting scheduled for Wednesday of an expert panel advising the agency on medicine applications.

The panel will vote on whether to recommend expanding use of the vaccine to children ages 6 months through 4 years, as well as expanding use of the Moderna vaccine to children 6 months through 5 years.

If the FDA clears the shots, a separate panel advising the Centers for Disease Control and Prevention is expected to meet to weigh the evidence. Many states and vaccination sites wait for the CDC to recommend vaccinations before rolling them out.

The FDA’s assessment of the Pfizer-BioNTech vaccine in young children, based on a study testing the shot or a placebo in 4,526 volunteers, was similar to its appraisal of Moderna’s shots in the age group.

One key difference: The FDA assessed three doses of the Pfizer-BioNTech vaccine in young children, compared with two doses for the Moderna vaccine in this age group.

“Given the uncertainty of the Covid-19 pandemic and likelihood of continued SARS-CoV-2 transmission during the ensuing months, deployment of the vaccine for use among children 6 months through 4 years of age will likely have a beneficial effect on Covid-19 associated morbidity and mortality in this age group,” the FDA staff wrote in their review.

The Pfizer-BioNTech vaccine was about 80% effective in preventing symptomatic Covid-19 among children ages 6 months through 4 years in a study conducted February through April, when the Omicron variant was prevalent in the U.S.

In comparison, the FDA found that Moderna’s vaccine was 37% effective for 2-to-5-year-olds and 51% effective for children 6 to 23 months, in a study conducted when the Omicron variant was predominant.

There were no reports of heart-inflammation conditions including myocarditis in children in the studies of the Pfizer-BioNTech and Moderna vaccines, the FDA said. The FDA has identified an elevated risk of the conditions in other subgroups, particularly males 12 to 17 years old.

The first two Pfizer doses are given three weeks apart, followed by a third dose at least eight weeks later. The two Moderna doses are given four weeks apart.

Children are generally at lower risk than older adults of developing severe Covid-19. Yet some have required hospitalization, especially during the winter wave of Omicron cases.

To reduce the risk of severe disease and protect more vulnerable adults, health authorities, pediatricians and infectious-disease specialists have encouraged vaccinating children.

Children 12 years and older have been able to get vaccinated for more than a year, while kids 5 to 11 years have been able since October 2021. They have also been able to get a booster shot. Yet the youngest children have had to wait for their initial shots.

Initially, Pfizer and BioNTech had tested two doses of the vaccine in the young age group. They found, however, that while the two-dose regimen induced the desired immune response in the youngest children—ages 6 months to 23 months old—it didn’t induce a strong immune response in children ages 2 to 4 years old.

In February, the FDA delayed a decision on whether to authorize the Pfizer vaccine for young children, saying it wanted to wait for the results of testing a third dose.

Some parents eager to vaccinate their young children have voiced frustration over the delays. A group called Protect Their Future in April filed a citizen petition with the FDA urging it to immediately review any application for use of a vaccine in children under 5.

Demand among eager parents is likely to lead to a rush to get some young children vaccinated as soon as doses become available.

Yet overall demand might be modest after that initial rush. A recent poll by the Kaiser Family Foundation found that only 18% of parents are eager to get their young children vaccinated right away. About 38% of parents of young children will wait and see before getting their kids vaccinated, while 27% will definitely not and 11% will do so only if required, the KFF poll found.

The FDA vaccine advisory panel also is meeting Tuesday to consider whether use of Moderna’s vaccine should be expanded to include children ages 6 through 17.

Write to Peter Loftus at peter.loftus@wsj.com