The New York Times first reported that the regulatory action was pending.
Families and pediatricians have been eager for a vaccine to become available for children, particularly in advance of the next school year.
Stephanie Caccomo, a spokeswoman for the FDA, declined to comment on the timeline.
“The FDA’s review of Pfizer’s request to amend its emergency use authorization (EUA) in order to expand the age range for its COVID-19 vaccine to include individuals 12-15 years of age is ongoing. We can assure the public that we are working to review this request as quickly and transparently as possible,” Caccomo said.
The FDA authorized the Pfizer-BioNTech vaccine for use in people 16 and older in December.
Pfizer announced at the end of March that it had submitted data from a trial of nearly 2,300 adolescents between 12 and 15 years old, half of whom had received the same two-shot regimen that has been shown effective and safe in adults.
The shot triggered stronger immune responses in the teens than those found in young adults. There were 18 cases of covid-19 in the trial, all of them among adolescents who received a placebo, suggesting the two-shot regimen offered similar protection to younger recipients as it does to adults.
Children are far less likely to suffer severe illness from covid-19, the infection caused by the virus. About 300 children have died in the United States, out of more than 576,000 total deaths.
Follow-on trials testing the Pfizer-BioNTech vaccine in younger children are ongoing.
The biotech company Moderna is conducting a similar trial of its vaccine in teens, with results expected in the summer. Moderna is also testing its vaccine in younger children. Johnson & Johnson is planning pediatric trials of its single-shot vaccine.
Dan Diamond contributed to this report.