Booster shots of the vaccines made by Pfizer-BioNTech or Moderna were 90 percent effective at preventing Americans infected with the Omicron variant from ending up in the hospital, according to data published on Friday by the Centers for Disease Control and Prevention.

Booster shots also reduced the likelihood of a visit to an emergency department or urgent care clinic. The extra doses were most effective against infection and death among Americans aged 50 and older, the data showed.

Over all, the new data show that the vaccines were more protective against the Delta variant than against Omicron, which lab studies have found is partially able to sidestep the body’s immune response.