The nation’s top public health official has given the green light to “mix-and-match” booster shots to increase antibodies to fight the coronavirus.

Under the decision from Centers for Disease Control and Prevention director Rochelle Walensky, eligible people can get any of the three available booster doses, regardless of which shot they received first. The Food and Drug Administration authorized the additional shots Wednesday. The CDC has also updated its guidance on boosters.

As cold weather and the holiday season approaches, boosters are especially important for older people and those with underlying conditions that put them at risk of severe infections.

“Winter is coming,” said Jeanne Marrazzo, director of the division of infectious disease at the University of Alabama at Birmingham. “We really want everybody to think about it like topping off your antibody levels, like topping off the tank before winter comes.”

Here’s what you need to know about mix-and-match booster shots.