EXPLAINER: Should you get a new COVID booster? If so, when?

John Wherry will wait until later in the fall to consider getting an updated COVID-19 booster. The University of Pennsylvania immunologist knows it's too soon after his shot late this summer, especially since he's not at high risk from the virus.

It’s the kind of calculation many Americans will face as booster shots that target currently circulating omicron strains become available to a population with widely varying risks and levels of immunity.

Here are some things to know:

HOW ARE THE NEW BOOSTERS DIFFERENT?

They’re combination or “bivalent” shots that contain half the original vaccine that’s been used since December 2020 and half protection against today’s dominant omicron versions, BA.4 and BA.5. It’s the first update to COVID-19 vaccines ever cleared by the Food and Drug Administration.

WHO’S ELIGIBLE?

Updated shots made by Pfizer and its partner BioNTech are authorized for anyone 12 and older, and rival Moderna’s version is for adults. They’re to be used as a booster for anyone who’s already had their primary vaccination series -- using shots from any U.S.-cleared company -- and regardless of how many boosters they’ve already gotten.

IF I JUST GOT ONE OF THE ORIGINAL BOOSTERS, SHOULD I GET THE NEW KIND RIGHT AWAY?

No. The FDA set the minimum wait time at two months. But advisers to the Centers for Disease Control and Prevention said it’s better to wait longer. Some advise at least three months, another said someone who’s not at high risk might wait as long as six months.

“If you wait a little more time, you get a better immunologic response,” said CDC adviser Dr. Sarah Long of Drexel University.

That’s because someone who recently got a booster already has more virus-fighting antibodies in their bloodstream....