Pfizer 3-dose COVID vaccine 80% effective against symptomatic omicron infection for youngest children

In long-awaited data, Pfizer said its three-dose vaccine was 80% effective against symptomatic omicron COVID-19 infection among children 6 months to under 5 years old.

The company cautioned that estimate was preliminary and could be adjusted as more data is collected. The trial wasn't big enough to estimate protection against severe disease, which experts expect to be higher.

For all age groups, vaccine efficacy against more mild breakthrough infections waned in the face of the highly transmissible omicron variant, but efficacy against severe disease and death remained high for most age groups.

Pfizer announced in December that it would not move forward with a two-dose vaccine after disappointing data, instead opting to study three doses for this age group. The company will submit the new data as part of its ongoing “rolling” submission to the FDA.

For anxious parents, the Pfizer news offers reassurance that the vaccine help protect young children currently not eligible for vaccination.

In the wake of Pfizer's new pediatric COVID-19 vaccine data, the Food and Drug Administration (FDA) has set a new, tentative date of June 15 for its advisers to discuss the COVID-19 vaccine applications for young children, meaning both vaccines could potentially be authorized by the end of June.

Pfizer also said its vaccine was safe, with a similar safely profile as placebo shots. If authorized, this vaccine would be three shots of 3 micrograms each. Each dose is one-tenth the adult dose.

Moderna's shot, if authorized, would be two doses, with each dose a quarter of the adult dose. Moderna is also studying a third shot for young children.

“We are pleased that our formulation for the youngest children, which we carefully selected to be one-tenth of the dose strength for adults, was well tolerated and produced a strong immune response,” said Albert Bourla, Pfizer's chairman and chief executive officer, in prepared remarks.

Moderna, meanwhile, asked the FDA for authorization on April 28 for a two-dose vaccine for this age range. Moderna’s preliminary analysis found its two-dose pediatric vaccine was 51% effective against symptomatic COVID-19 among children 6 months to under 2 years old, and 37% among children 2 to 5 years old -- roughly the same efficacy seen in adults during the omicron surge. Protection against serious disease and death was higher.

"I anticipate a lot of parents will be asking whether they should choose a two-dose Moderna vaccine or the three-dose Pfizer vaccine," said Dr. Alok Patel, pediatric hospitalist at Stanford Children's health and an ABC News contributor. "I would recommend that parents pay attention to the FDA and CDC’s guidance and what final analysis reveals for both vaccines."

Experts caution that vaccine efficacy against symptomatic infection is a high bar, and experts expect these vaccines will offer excellent protection against severe illness, just as they do for adults.

Though children under five is the last remaining age group that’s yet to be vaccinated, polls indicate there could be sluggish uptake.

A recent survey from KFF found that just under 1 in 5 parents are eager to get their children under five vaccinated right away.

However, the KFF poll more than half of parents said that they feel they do not have enough information about the vaccines’ safety and efficacy for children under age 5 — which could change after the public FDA advisory meetings to discuss the pediatric data.

"Parents should also be aware that this preliminary data will be supplemented by additional data in June, which will then be thoroughly reviewed by both the FDA and the CDC," Patel said.