Medical Technology

Pfizer COVID Vaccine for Younger children who hit snag

Editor’s note: Find the latest COVID-19 news and guidance in Medscape’s Coronavirus Resource Center.

Dec. 17, 2021 — Pfizer’s COVID-19 vaccine for children ages 2 to 5 years old fizzled in clinical trials, the company said on Friday, signaling a further delay in getting a vaccine to preschoolers just as Omicron bears down on the U.S.

In a news release, Pfizer reported that while its 3-microgram dose — which is less than one-third of the dose given to older children — generated a protective immune response in babies and toddlers ages 6 to 24 months, it didn’t generate adequate immunity in children ages 2 to 5.

The company plans to change its clinical trial to add a third dose for younger children in hopes of improving those results. It also plans to test a third dose of its 10-microgram vaccine for children ages 5 to 12.

If the trials are successful, Pfizer said it would submit data to the FDA for an emergency use authorization (EUA) in the first half of 2022.

That pushes the timeline of getting a vaccine to younger children back by several months. In November, Anthony Fauci, MD, head of the National Institute of Allergy Infectious Diseases, predicted a vaccine would be ready for preschoolers by spring.

“On one hand, parents are understandably disappointed,” said Jill Foster, MD, a pediatric infectious disease doctor at the University of Minnesota Medical School. “On the other, it shows that the system for testing vaccines is working. Children are not little adults and have complex immune systems, so it’s not just a matter of making the dose smaller and expecting that it will work,” she said, noting that data from Moderna’s KidCOVE study in preschoolers is pending.

Until there’s a vaccine, Foster says parents should protect babies and toddlers by making sure everyone around them is vaccinated, promote the use of face masks for everyone around them and for all children over age 2, and continue to avoid crowded gatherings, particularly those that are indoors.

“Hand sanitizer is important, but this virus, especially the Omicron variant, is very easily spread through the air, so keep the air clear of virus as much as possible,” she said.

While the youngest children are still waiting for an effective vaccine, there was reassuring news Thursday about the safety of Pfizer’s vaccine for school-aged kids — those ages 5 through 11.

Out of more than 7 million doses given since this vaccine was authorized for emergency use in late October, most reactions to the vaccine — including arm pain, swelling, and fatigue — have been mild and gone away quickly, without the need to miss school or see a doctor, the CDC reported to a meeting of its Advisory Committee on Immunization Practices, or ACIP, on Thursday.

Many experts had been waiting to see if this vaccine would cause rare cases of heart inflammation called myocarditis, as a higher dose did in teens and young adults.

The news on this front was excellent. About 6 weeks after this vaccine became available, the CDC says there have been only eight confirmed cases of myocarditis in this age group. Six more cases are under investigation.

To put this risk into context, data collected by the American Academy of Pediatrics and the Children’s Hospital Association shows that about 1% of children who test positive for COVID-19 are hospitalized for their infections, while the risk of getting a case of myocarditis after vaccination is .0002%, making it about 5,000 times more likely that a child would need to be hospitalized for COVID-19 than for myocarditis after vaccination.

John Su, MD, who is a member of the CDC’s Vaccine Safety Team, reported there had been two deaths in children after a COVID-19 vaccination. Both were girls, ages 5 and 6. Both had complicated medical histories for several medical disorders. It’s not clear their deaths were linked to the vaccine, and the causes of their deaths are still under investigation.


Jill Foster, MD, pediatric infectious disease doctor, University of Minnesota Medical School, Minneapolis.

John Su, MD, Vaccine Safety Team, CDC COVID-19 Vaccine Task Force.

CDC Advisory Committee on Immunization Practices, Dec. 16, 2021.

News release, Pfizer, Dec. 17, 2021.

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