A three-dose regimen was 80.3% effective in a preliminary finding based on 10 infections in children ages 6 months through 4 years old, the vaccine partners said in a statement on Monday. A formal analysis will be done once 21 children are infected, as the study was designed, and final efficacy data will be shared when available. 

The initial findings are likely to be welcome news to parents and health officials who are anxious to protect the youngest children as infections are on the rise and mitigation measures are dropped in many places. The lack of a vaccine for infants, toddlers and preschoolers for nearly a year and a half after shots first became available has created a conundrum for families who are trying to protect their young children while much of life has returned to normal. 

Pfizer and BioNTech expect to submit the necessary data to U.S. regulators this week to secure an emergency-use authorization for young children, after starting the process in February. They will ask other regulators around the world for clearance in the coming weeks, they said. 

Shares of Pfizer rose 1.1% at 10:09 a.m. in New York on Monday, while BioNTech’s American depository receipts were flat.

One-tenth dose

In the clinical trial, 1,678 children were given three shots of a 3 microgram dose of the vaccine, one-tenth the amount given to adults. They developed a strong immune response following the third dose, which was administered at least two months after the second shot, the companies said. The vaccine was well tolerated, with a safety profile similar to that of the placebo. Most side effects were mild or moderate.

The vaccine efficacy was determined by comparing the number of COVID cases among those who received the active immunization to those who got the placebo. Researchers determined it was 80.3% effective based on an analysis of 10 symptomatic Covid cases identified at least seven days after the third dose was given. 

Pfizer Chief Executive Officer Albert Bourla said the drugmaker is moving quickly to get the shots to young kids.

“We look forward to soon completing our submissions to regulators globally with the hope of making this vaccine available to younger children as quickly as possible,” he said in the statement.

Frustrated parents

Much to the frustration of parents, Pfizer and BioNTech’s pediatric trial had faced months of delays. The companies initially studied a two-dose regimen in children under 5 that wasn’t clearly effective against the highly-transmissible Omicron variant. At the request of US regulators, they shifted to study three shots instead, extending the amount of time it took to complete the trial.

In an analysis of select participants, the three-shot regimen prompted an immune response in children aged 6 months through 4 years after one month that was about as strong as two doses in those 16- to-24-years old, the companies said. 

Meanwhile, Moderna Inc. has said that a two-dose regimen of its vaccine in kids aged 6 months to 5 years was modestly effective without any serious safety concerns. It didn’t pass the 50% efficacy threshold regulators have typically looked for in approving COVID vaccines.

The U.S. Food and Drug Administration will convene an advisory committee meeting on June 15 to discuss the risks and benefits of the Moderna and Pfizer-BioNTech vaccines in the youngest children. The panel of experts will provide a recommendation as to whether or not they should be cleared for emergency use. One day prior, the FDA will convene a meeting to discuss Moderna’s emergency-use request for its vaccine in children ages 6 through 17 years old. 

Even if cleared, the pediatric vaccine campaign may be challenged by hesitant parents. Only 29% of children ages 5 through 11 have been fully vaccinated in the U.S. so far, according to data from the Centers for Disease Control and Prevention. Adolescent uptake is markedly better, though not yet on par with adults, with 59% of those ages 12 through 17 fully vaccinated. Demand for the shot among school-aged children has tapered off in recent months.