Pfizer/BioNTech's new paediatric COVID-19 vaccine vials are seen in this undated handout photo. Image Credit: REUTERS

WASHINGTON: The US federal regulators evaluated for the first time on Friday the safety and efficacy of a coronavirus vaccine for children ages 5-11, saying that the benefits of staving off COVID-19 with the Pfizer-BioNTech vaccine generally outweighed the risks of the most worrisome possible side effects in that age group.

The analysis came on the same day that the Food and Drug Administration posted data from Pfizer showing that the vaccine had a 90.7% efficacy rate in preventing symptomatic COVID-19 in a clinical trial of 5- to 11-year-olds.

The findings could add momentum for FDA authorisation of the paediatric dose on an emergency basis, perhaps as early as this week, opening up a long-awaited new phase of the nation’s vaccination campaign. The agency’s independent vaccine expert committee is set to vote Tuesday on whether to recommend authorization.

In a briefing document posted on the FDA website, the agency said it had balanced the dangers of hospitalization, death or other serious consequences from COVID-19 against the risk of myocarditis. A rare condition involving inflammation of the heart muscle, myocarditis has been linked to the Pfizer-BioNTech and Moderna vaccines, especially among young men.

“The overall analysis predicted that the numbers of clinically significant COVID-19-related outcomes prevented would clearly outweigh the numbers of vaccine-associated excess myocarditis cases,” regulators wrote.

As is customary before a vote of the FDA’s advisory committee, the regulators took no stance on whether the new use of a vaccine should be authorized.

If the FDA rules in favour of authorization and the Centres for Disease Control and Prevention and its own panel of vaccine experts agree, the 28 million children in that age group could become eligible for shots in the first week of November.

Encouraging data

“There’s a lot of data to be encouraged by,” said Dr. Kathryn M. Edwards, a professor of paediatrics in the division of infectious diseases at Vanderbilt University School of Medicine. She said the results exceeded the protection offered by the best flu vaccine and could eventually lead to the easing of restrictions intended to prevent elementary school children from contracting the virus.

Pfizer and BioNTech announced a month ago that their vaccine worked well for young children, but no comprehensive clinical data was released publicly until Friday. Children in the trial received two doses of 10 micrograms - one-third of the adult dose - three weeks apart. Researchers said that the dosage was safe, and that trial participants had seen only mild side effects.

Of 2,268 children in the trial, twice as many were given the vaccine as received a placebo. Sixteen children who received the placebo got COVID-19, compared with three who received the vaccine. All of the COVID cases occurred in July or later, as the highly transmissible delta variant was spreading in the United States and globally, according to the company. The FDA said it could not determine whether the cases were caused by the delta variant.

Pfizer said it had follow-up safety data for an additional 2,250 children, but only for a median of 2 1/2 weeks after they received a second dose.

There were no cases of severe COVID among trial participants, and no cases of two rare heart conditions that have been linked to the vaccine in teenagers and adults, especially young males. But the trial was likely not big enough to detect whether those particular conditions - myocarditis and pericarditis - might appear with any frequency in younger children.

Minor side effects in the study group generally occurred more frequently after the second dose, the FDA reported; the most common were pain at the injection site, fatigue and headache.

The FDA modelled different scenarios with varying levels of viral spread to determine the number of symptomatic COVID cases, including severe ones, that would be prevented by the vaccine. They balanced that against the risks from myocarditis and pericarditis cases associated with vaccination.

Even given a low rate of COVID infections, they said, the benefits of vaccination could outweigh the risks because the virus could lead to more serious health consequences than any side effects.

Researchers looked at immune responses, comparing them with levels in adults who had received the vaccine. Pfizer then deduced that the protection afforded by the lower dose in children could be as substantial as that afforded by the higher dose in adults. That approach is particularly important in small trials.

After the second shot, the children had levels of neutralizing antibodies that were at least equal to those of 16-to-25-year-old volunteers in another Pfizer-BioNTech trial. Although antibody levels are just one measure of the immune system’s response, experts have said such a finding would indicate that one-third of an adult dose was the proper dosage for young children.

Studies have shown that the risk of developing myocarditis or pericarditis from COVID-19 is higher than from vaccination. Still, some countries have recommended a single dose of the Pfizer-BioNTech vaccine for children 12 and older, offering less protection but possibly with a lower risk of side effects.

Experts will almost certainly raise concerns about those side effects at the FDA advisory committee meeting, according to Dr. H. Cody Meissner, a member of the panel and chief of the Division of Pediatric Infectious Diseases at Tufts Children’s Hospital in Boston.

“I certainly hope that we’re in a position to recommend this, because people are certainly waiting for it, they’re anxious to have it,” he said. “But our responsibility is to balance both risk and benefit.”

Vaccine experts have said that Pfizer’s lower dosing could mitigate risks. “We always like to use the least amount of vaccine that’s needed to generate an immune response,” Edwards, the Vanderbilt expert, said, “because it’s generally associated with fewer adverse events.”