HomeHealthFDA advisers are recommending that the agency license Moderna and Pfizer's long-awaited...

FDA advisers are recommending that the agency license Moderna and Pfizer’s long-awaited Covid vaccines for young children.

After two doses, Pfizer’s vaccine was only 28 percent effective in preventing symptomatic infections in children 6 months to 4 years of age. Pfizer suggested the vaccine was 80 percent effective after a third dose, but the finding was based on just 10 cases from a subset of the 1,678 trial participants. The trial protocol specified that assessments of vaccine efficacy be based on at least twice as many cases; the small number of cases on which the efficacy finding was based was cause for consternation among committee members and regulators on Wednesday.

Dr. Doran Fink, a top federal vaccine regulator, called Pfizer’s efficacy data preliminary. “We consider it to be imprecise and potentially unstable,” he said. “Exactly how effective the vaccine is after the third dose needs more data.”

Moderna found its vaccine to be 51% effective in preventing symptomatic infections in children 6 months to 2 years old, and 37% effective in children 2 to 5 years old. Those results appear consistent with those reported in studies of adults during the Omicron era, the FDA said. Still, immunization continues to offer strong protection against serious illnesses that lead to hospitalization and death.

Regulators and company officials spent part of the day discussing side effects caused by vaccines. The vast majority were mild and tolerated by children in clinical trials: irritability and crying, drowsiness, fatigue, and loss of appetite. A smaller number of trial participants suffered from fever, but that was consistent with the effects of other pediatric vaccines.

In younger age groups, fevers can be more debilitating and require more urgent medical attention, a dynamic that puts significant pressure on manufacturers to calibrate dosage correctly. Pfizer chose a dose just one-tenth the adult dose, given as three injections; the first two are given three weeks apart, with the third arriving at least eight weeks after the second. Moderna used a quarter strength of its adult dose, given as two injections, four weeks apart.

Some tough questions remain. It is important to note that none of the vaccines have been tested against the subvariants circulating in the United States. Clinical trials were largely conducted when the Omicron variant was prevalent. Two subvariants, BA.4 and BA.5, could become dominant within a month.

The need to protect these children from Covid is great, Dr. Peter Marks, the FDA’s chief vaccine regulator, said at the meeting. He added that hundreds of children had died of Covid, a rate that he said “compares terribly” with pediatric deaths during a flu surge in 2009 and 2010.

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