(NEXSTAR) – As more and more Americans become eligible for a booster shot of the COVID-19 vaccine, they’ll be faced with a choice: Which kind should they get?

The Food and Drug Administration and the Centers for Disease Control have both given mixing and matching vaccine types the green light. That means you don’t have to pick the same brand for your booster shot as you got for your first round of vaccination.

But just because you can switch things up, doesn’t mean you should. We asked doctors when mixing and matching makes sense, and when it doesn’t.

If you received the Johnson & Johnson vaccine

Anyone 18 and older who received a Johnson & Johnson vaccine more than two months ago is now eligible for a booster shot.

We asked Dr. Bob Wachter, chair of the Department of Medicine at the University of California, San Francisco, what he would do if he were a J&J recipient: get another J&J dose or get a different type?

“No question: I’d get an mRNA,” Wachter said.

“Personally, I would opt to get one of the mRNA vaccines,” agreed Dr. Jaquelin Dudley, associate director of the University of Texas’ LaMontagne Center for Infectious Disease.

The doctors’ answers are informed by several studies that show both Pfizer and Moderna, the mRNA vaccines, offer a stronger antibody response and therefore more protection against COVID-19.

If he had the choice between Moderna or Pfizer for a booster, Wachter said he’d probably opt for Moderna.

“Moderna seems to lead to slightly higher antibodies after J&J,” Wachter said. “It’s not certain that that correlates with level or duration of protection, but it seems logical that it would.”

If you received Pfizer or Moderna

If you got Pfizer or Moderna for your first two shots, you’re eligible for a third shot if it’s been six months since your last dose and:

• You’re 65 or older
• Or you have a medical condition that makes you more vulnerable to COVID-19
• Or your occupation exposes you to a higher risk of catching COVID-19

Pfizer and Moderna recipients also have the choice to mix and match, but they have less of a reason to.

“I doubt that there is any real benefit to receiving a different type if you already got an mRNA vaccine,” said Dudley.

“There is weak evidence that using the other mRNA might lead to a slightly stronger response,” said Wachter, but both doctors said the only serious reason you might want to switch vaccine types in this scenario is if you’re worried about side effects.

If you had an adverse reaction to Moderna the first time around, you might want to talk to your doctor about getting a Pfizer booster instead (and vice versa). But if you tolerated the vaccine you got the first time around, there’s not a real reason to risk switching vaccine types and taking the “minuscule” risk that you’ll have a bad reaction to something new, Wachter said.

“The Moderna booster will be given as a half-dose of the original two-shot regimen, but it is not clear if that will reduce side effects (assuming that you had any previously),” added Dudley.

“In the end, I don’t think it matters,” said Wachter. “Certainly, since Moderna has proven to be a bit stronger than Pfizer, if I got Moderna I’d take another Moderna (unless for some reason it wasn’t available).”

That being said, Wachter said he got Pfizer his first two shots, and opted to get Pfizer for his booster shot, as well. “I think it’s really a toss-up,” he said.