As outside advisors to the Food and Drug Administration on Wednesday evaluated the Moderna and Pfizer-BioNTech coronavirus vaccines for very young children in the United States, the panel focused on how the shots differed as part of a long-awaited review that could pave the way for regulators to grant emergency authorization this week for one of the vaccines or both.
The US Food and Drug Administration said clinical trial data from the companies shows that each vaccine met standards for safety and efficacy in the age group. The agency has sent 230 pages of documents to the consultants for their review. A vote on whether to recommend approval of the Pfizer vaccine for children 6 months to 4 years old, and Moderna for children 6 months to 5 years old, is expected to be voted on by the end of Wednesday. (Watch the meeting live here.)
More than two years into the pandemic, no vaccine has been authorized for children under the age of 5 in the United States, an unmet need that has troubled many parents. If the committee recommends one or both of the two vaccines, the Food and Drug Administration is preparing to remove them as early as Friday.
Regulators and company officials spent most of the morning discussing the side effects caused by the vaccine, the vast majority of which were mild and tolerated by children in clinical trials: irritability, crying, drowsiness, fatigue and loss of appetite. Fewer participants in the trial experienced fevers, most of which did not exceed severe levels.
In younger age groups, fevers can be more subdued and require more urgent medical attention, a dynamic that places significant pressure on manufacturers to properly calibrate doses. Pfizer selected a dose that was one-tenth the strength of an adult dose, in three shots; The first two weeks are given every three weeks, and the third comes at least eight weeks later. Moderna used a quarter of the strength of its adult doses, in two doses, four weeks apart.
Some difficult questions remain. Perhaps most importantly, neither vaccine has been tested against the sub-variants prevalent in the United States. Clinical trials were largely conducted when the Omicron variant predominated. Two sub-variables, BA.4 and BA.5, can become dominant within a month.
The need to protect these children from Covid is remarkable, Dr. Peter Marks, the FDA’s top vaccine regulator, said at the meeting. He added that hundreds of children died of Covid, a rate he said “compared terribly” to child deaths during the major flu wave in 2009 and 2010.
Both vaccines in Wednesday’s study appeared to be significantly less effective against symptomatic infections than the adult vaccine when they were introduced. The U.S. Food and Drug Administration (FDA) credits Omicron as being more adept at evading vaccines’ defenses against infection than the original version of the virus.
Given the marked waning of protection among adult recipients and the rapid evolution of the virus, organizers said that children who will receive the Pfizer and Moderna vaccines will likely need a booster dose. This means that the Pfizer vaccine, which was developed with Germany’s BioNTech, could end up with four doses, while Moderna’s vaccine could be three.
The Pfizer-BioNTech and Moderna vaccines raised levels of neutralizing or virus-blocking antibodies in children similar to those in adolescents and young adults 16 to 25 years old. The Pfizer vaccine has been licensed for children ages 5 to 15 since last year, and regulators said it helped prevent hospitalizations and deaths.
After two doses, Pfizer’s vaccine was only 28% effective in preventing symptomatic infections in children 6 months to 4 years old. Pfizer suggested the vaccine was 80 percent effective after a third dose, but the result was based on just 10 cases from a subset of 1,678 trial participants. The trial protocol specified that evaluations of vaccine efficacy are based on at least twice as many cases; The small number of cases on which the outcome of the event was based was a cause of panic among committee members and organizers on Wednesday.
Dr. Doran Fink, the chief federal vaccine regulator, described Pfizer’s efficacy data as preliminary. “We consider it inaccurate and potentially unstable,” he said. “What exactly is the efficacy of the vaccine after the third dose needs more data.”
Moderna found its vaccine to be 51 percent effective in preventing cross-infection in children 6 months to 2 years old, and 37 percent effective in children 2 through 5. These results appear to be consistent with those reported in studies conducted on adults during the omicron era, according to the U.S. Food and Drug Administration. He said. However, immunization continues to provide powerful protection against severe illness leading to hospitalization and death.
On Wednesday, a panel member asked if there was evidence of how children who have recovered from the virus would respond to a vaccine — a common question among parents.
A Moderna official said the company’s study showed that young children who got Omicron and were vaccinated had higher levels of protection, a conclusion supported by outside research.
Although Moderna’s efficacy data appeared to be somewhat stronger than that of Pfizer’s, scientists have cautioned strongly against such comparisons.
“These are different populations. The studies were conducted at different times. Scientifically, we don’t have a direct comparison,” said Dr. Jesse L. Goodman, former chief scientist of the Food and Drug Administration.
June 15, 2022
Due to an editorial error, an earlier version of this article erred when the Pfizer-BioNTech vaccine was licensed for various age groups in the United States. The vaccine was licensed for ages 16 and older in late 2020, not in 2021, when vaccines were licensed for ages 5 to 15.