The U.S. Food and Drug Administration has authorized an optional second round of COVID-19 booster shots for anyone 50 and older who wants extra vaccine protection.

The authorization for the Pfizer-BioNTech and Moderna shots comes as the new omicron subvariant continues to rapidly spread overseas and raise concern that it may lead to a similar increase in infections in the U.S. COVID-19 cases, hospitalizations and deaths have been falling in the U.S. in recent weeks.

The new subvariant, BA.2 , is more transmissible than the original omicron variant, which caused a record number of cases in the U.S. in January. It does not appear to be more severe in terms of illness, however.

A second booster shot is not being recommended to everyone over the age of 50 at this time.