The federal government plans to test new vaccines that combine multiple strains of the virus to find what offers the broadest coverage, a senior Biden administration official told Axios. The goal is to increase the odds of having a shot ready that works against whatever strain comes next.

State of play: Fourth doses are already authorized for immunocompromised people. However, for most people, data suggests that a single booster shot offers strong protection against severe disease, including from Omicron.

But the big question is how long that protection against hospitalization and death will last.

The U.K. recently decided that it will soon offer fourth shots to the elderly and some people with health conditions, per The Sunday Times.