https://www.siliconvalley.com/2021/08/23/covid-fda-cautions-against-off-label-use-of-pfizer-vaccine-in-younger-children/

(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.