(CNN) Even though the US Food and Drug Administration has fully approved the Pfizer/BioNTech Covid-19 vaccine for people age 16 and older, and it remains authorized for people as young as 12, the agency is warning against using the vaccine "off-label" in children younger than 12. To do so, it says, "would not be appropriate."
Off-label refers to an approved product being used in a way or in a patient that it wasn't necessarily approved for; it happens commonly with some drugs, such as when a chemotherapy approved for one type of cancer is used to treat a different type.
The Pfizer/BioNTech Covid-19 vaccine is not currently approved nor authorized for children younger than 12, and the appropriate dosage for this age group has yet to be determined.
"We do not have data on the proper dose nor do we have full data on the safety in children younger than what is in the EUA," Acting FDA Commissioner Dr. Janet Woodcock said during a briefing call on Monday.
"So that would be a great concern that people would vaccinate children because we don't have the proper dose and we don't have the safety data, nor do we have all the efficacy data, as well," Woodcock said. "We are not recommending that children younger than age 12 be vaccinated with this vaccine. It would not be appropriate."
Meanwhile, the FDA and the American Academy of Pediatrics (AAP) both strongly recommend that all eligible adolescents, ages 12 to 17, be vaccinated as soon as possible, especially as the highly transmissible Delta coronavirus variant continues to circulate nationwide.
As of last week, the AAP reports 180,000 new cases of Covid-19 among children and adolescents, according to the Academy.
So far, about 8.5 million or 34% of all adolescents ages 12 to 17 are fully vaccinated against Covid-19.
It's clear many parents are eager to get younger children vaccinated, but FDA's Woodcock said that children "are not just small adults."
"We really would have to have the data and the appropriate dose before recommending that children be vaccinated," Woodcock added on Monday.
The AAP also "strongly discourages" using the vaccine off-label in children younger than 12, noting that the dose of the adult vaccine is much higher than the doses being tested in young children.
"The clinical trials for the COVID-19 vaccine in children ages 11 years old and younger are underway, and we need to see the data from those studies before we give this vaccine to younger children," AAP President Dr. Lee Savio Beers said in a statement on Monday, following the FDA's approval.
"The dose may be different for younger ages," Beers said. "The AAP recommends against giving the vaccine to children under 12 until authorized by the FDA."
Dr. Yvonne Maldonado, chair of the AAP Committee on Infectious Diseases, also urged physicians to wait until clinical trials are complete in young children before giving the vaccine to those under 12.
"We do not want individual physicians to be calculating doses and dosing schedules one-by-one for younger children based on the experience with the vaccine in older patients," Maldonado said in a statement on Monday.
"We should do this based on all of the evidence for each age group, and for that we need the trials to be completed. I know parents are anxious to protect their children, but we want to make sure children have the full benefit of ongoing clinical trials."
In a letter sent to Woodcock earlier this month, the AAP called on the FDA to work aggressively to authorize a vaccine for children younger than 12.
Pfizer has said it expects to have vaccine trial data on children ages 5 to 11 by the end of September, and the company could apply to have its vaccine authorized for those younger ages shortly after. The company also has said data for even younger children, ages 2 to 5, could be available shortly after.
Moderna and Johnson & Johnson are also working on studies in children.
Last month, the FDA asked Pfizer and Moderna to double the number of children ages 5 to 11 in clinical trials. The FDA also asked for six months of follow-up safety data, instead of the two months it asked for with adults.
"We know parents are eager to be able to give their children the protection of this vaccine, and the American Academy of Pediatrics shares that feeling of urgency," Beers said on Monday. "The Delta variant has led to significant increases in the number of children and adults infected with the virus. While we wait for a vaccine to be authorized for younger children, it's important that everyone who is eligible now get the vaccine. That will help reduce the spread of the virus and protect those who are too young to be vaccinated."