In October, the Centers for Disease Control and Prevention recommended that high-risk adults get a second updated Covid vaccine to bolster their protection against the virus.

The agency now recommends that people ages 65 and up and those with weakened immune systems get a second dose of the 2024-25 vaccine six months after their first dose.

It’s not the first time the agency has advised or allowed for an additional dose for at-risk groups several months after the first. In the spring of…