U.S. regulators authorized a second booster dose of Pfizer Inc (PFE.N) and BioNTech SE’s (22UAy.DE) COVID-19 vaccine for people 50 and older due to concerns about waning immunity in the age group, the drugmakers said on Tuesday.

The U.S. Food and Drug Administration also authorized the second booster dose of the vaccine for people aged 12 and older with compromised immune systems. The authorization comes as some scientists have raised concerns about the highly contagious BA.2 Omicron subvariant, which has driven new spikes in COVID-19 cases in other countries.

Pfizer and BioNTech originally asked for the next booster doses to be authorized for people 65 and older in a submission citing data collected in Israel, where a second booster is already authorized for many people over age 18. The companies did not explain why the age range had been expanded. Read more here.