CNN  — 

Now that the United States has started rolling out child doses of the Pfizer/BioNTech coronavirus vaccine for children ages 5 to 11, many parents are wondering when shots could be available for even younger kids.

US health officials estimate that could be next year.

“We’re probably a few more months off for the younger children,” Dr. Peter Marks, director of the US Food and Drug Administration’s Center for Biologics Evaluation and Research, said during a video call with reporters last week.

That means early 2022 at the soonest.

Of the three companies with authorized Covid-19 vaccines in the US, Pfizer is furthest along in testing shots for children under the age of 5.

Moderna is studying its coronavirus vaccine in children younger than 12. Johnson & Johnson has planned trials in those younger ages but hasn’t started yet.

The FDA will want much more safety data for the younger children, Marks said.

“It has to do with when they were enrolled in the trials, and the fact that as we get down to younger children, the benefit-risk gets to be even more of a careful consideration, because the youngest children are affected the least directly in terms of severe Covid-19,” Marks said. “We want to have robust safety data sets.”

Where each vaccine maker is on shots for younger ages

The Pfizer/BioNTech studies are in two young age groups: children ages 2 to 5 and those 6 months to 2 years old. Both age groups are in Phase 2/3 trials, a Pfizer company spokesperson confirmed Wednesday.

Pfizer and BioNTech hope to have initial data for ages 2 to 5 by the end of the year.

The companies would need to submit their clinical trial data to the FDA to apply for emergency use authorization of their vaccine for children younger than 5. Once the FDA authorizes the vaccine for these younger ages, the US Centers for Disease Control and Prevention would need to recommend it before shots can go into arms.

“The Food and Drug Administration and CDC won’t approve the vaccine until there’s some data showing safety and efficacy,” Dr. Philip Landrigan, a pediatrician and immunologist at Boston College, told CNN on Wednesday.

“There’s every reason to think that it will be safe, and it will be efficacious,” Landrigan said. “But the agencies need to be cautious, justifiably so, and so they’re not going to give the approval until they have the data.”

Pfizer and BioNTech announced last week that the United States has purchased 50 million more doses of the companies’ coronavirus vaccine and “will receive these additional doses to continue to support preparedness for pediatric vaccinations, including securing vaccines for children under 5 years of age, should they receive regulatory authorization.”

Pfizer and BioNTech noted that they expect to deliver those doses by April 30 next year.