Scientific advisers from the Centers for Disease Control and Prevention met Saturday to decide whether the benefits of Covid vaccines outweigh the risks for children under 5, the last Americans eligible for the injections.
The meeting, broadcast live here, started at 10 a.m. Dutch time. The advisors were expected to vote yes, despite concerns about the lack of data, especially regarding the efficacy of the Pfizer-BioNTech vaccine.
Earlier this week, another panel of experts advising the Food and Drug Administration unanimously supported the vaccines. The FDA on Friday approved the Moderna vaccine for children 6 months to 5 years of age and the Pfizer vaccine for children 6 months to 4 years of age. (The Pfizer-BioNTech vaccine has been available for children ages 5 and older since November.)
On Friday, CDC advisers heard evidence supporting the effectiveness of the vaccines in the youngest children. But the committee repeatedly pressed Pfizer to its estimates, noting that three doses of that vaccine would be needed to protect children, compared to two doses of the Moderna vaccine.
Both vaccines are safe and both produced antibody levels comparable to those seen in young adults. If the commission’s approval is swiftly followed on Saturday by a green light from the agency’s director, Dr. Rochelle Walensky, states are preparing to begin immunizing the children next week.
One of the tasks facing the CDC panel on Saturday is the difficulty of recommending two very different vaccines for the same population.
“Implementing these two implementations will be incredibly challenging,” said Katelyn Jetelina, a public health expert and author of the widely read newsletter “Your Local Epidemiologist.”
“There will be a lot of proactive communication about the difference between the two and the implications of adopting one over the other,” she said.
In his clinical trials, Moderna found that two injections of its vaccine, each at one-fourth the adult dose, produced antibody levels at least as high as those seen in young adults.
The company estimated the effectiveness of the vaccine against symptomatic infection at about 51 percent in children aged 6 to 24 months and 37 percent in children aged 2 to 5 years. The side effects were minor, although about one in five children had a fever.
Based on that data, the FDA approved two injections of the Moderna vaccine, four weeks apart.
The Pfizer-BioNTech vaccine also elicited a strong immune response, but only after three doses, company officials told scientific advisers Friday.
Two doses of the vaccine were inadequate, they said, justifying the FDA’s February decision to delay approval of the vaccine until regulators had data on three doses. Two doses may not have been enough because the company gave the children only one-tenth of the adult dose by injection, some advisers said.
The vaccine has an overall efficacy of 80 percent in children under the age of 5, Pfizer scientists said on Friday. But that calculation was based on only three children in the vaccine group and seven who received a placebo, making it an unreliable measure, the CDC advisers noted.
“We just have to assume we don’t have efficacy data,” said Dr. Sarah Long, an infectious disease expert at Drexel University College of Medicine. But dr. Long said she was “easy enough” with other data supporting the vaccine’s potency.
Three doses of the Pfizer vaccine produced antibody levels comparable to those seen in young adults, suggesting it is likely just as effective.
“The Pfizer is a three-dose series, but as a three-dose series, it’s quite effective,” said Dr. William Towner, who led the vaccine trials for both Moderna and Pfizer at Kaiser Permanente in Southern California.
Any vaccine would be better than none, added Dr. Towner to it. He predicted that some parents might opt for Moderna because it is easier to take children to a pediatrician for two injections than to make sure they receive three doses.
The Pfizer vaccine was approved in November for children ages 5 to 11, but less than 30 percent in that age group have received two injections. Parents of the youngest children may be more willing to opt for a Covid vaccine if it can be offered alongside other routine immunizations, said Dr. towner.
“That’s the area that a lot of people aren’t sure about right now,” he said. “I hope some guidance will be offered.”