A panel of outside experts is due to vote on Tuesday on whether the FDA should authorise the jab for children aged between five and 11, the first Covid-19 vaccine for this age group.
However, the FDA believes that if the number of myocarditis cases observed in the younger age group is similar to that seen in vaccinated 12- to 15-year-olds, the number of Covid-19 related hospital admissions prevented will outnumber those caused by myocarditis.
Pfizer suggested the rate of myocarditis in younger children was likely to be lower than for 12- to 15-year-olds, in part because they will get a lower dose.
If the FDA does approve the jab, it could be made available as early as next month. It is already in use for people aged 12 and older.
In Pfizer’s recent trial, five- to 11-year-olds were given two shots of a 10-microgram dose, one-third of that given to the over-12s.
Sixteen children in the trial who had received a placebo got Covid-19 against three who were vaccinated. Because more than twice as many children in the 2,268-participant study were given the vaccine than placebo, that equates to better than 90 per cent efficacy.
Pfizer and BioNTech said last month that their Covid-19 vaccine induced a robust immune response in the children, and FDA staff now say it meets the agency's criteria for immune response.
Pfizer has now expanded its trial, and the drug firm said the adverse event profile in the larger group did not suggest any new safety concerns from the vaccine.
The second cohort of children has been observed for a shorter time. All of them had received their second dose, more than 70 per cent of them at least two weeks ago.
About 190 million people in the US are fully vaccinated, including more than 11 million aged 12 to 17 who have received the Pfizer jab.
Additional reporting by ReutersInternet Explorer Channel Network