Is this year's COVID booster a good match for new variants?

(NEXSTAR) – Depending on when you last got vaccinated, that COVID-19 shot may no longer be a good match for the variants expected to dominate this fall and winter.

As a virus circulates, it continues to mutate. Some mutations can make it spread faster, others make symptoms feel stronger, and some changes make it better at evading your pre-existing immunity.

This year's new batch of shots, reformulated and released over the past two months, are a "fairly good match" to the predominant variants infecting people right now, said Dr. Andrew Pekosz, professor at Johns Hopkins Bloomberg School of Public Health, in a recent media briefing.

"They're never a perfect match because the vaccine strain choice is made back in June and while the vaccine doesn't change, the virus keeps replicating and the virus keeps mutating," he said.

The updated Moderna and Pfizer shots target the KP.2 variant, known as one of the FLiRT subtypes of omicron. The Novavax booster targets the JN.1 strain.

Both of those strains were dominant earlier this year, when the pharmaceutical companies were manufacturing these new doses, but are no longer as prominent. Now, the KP.3 and KP.3.1.1 types are more common.

While they may not be a perfect match, the latest variants have enough in common with the KP.2 and JN.1 that the boosters should still offer effective cross-protection.

Plus, the 2024 editions of the vaccine are a much better fit than what we had available this time last year, which were targeting the original omicron strain.

"These new strains are as different from [the original] omicron as omicron was from the ancestral strain. They’re pretty far apart evolutionarily," explained Dr. Dean Blumberg, chief of pediatric infectious diseases at UC Davis Health. "The updated vaccine is a much better match for the currently circulating variant. That match is about 80 percent. We expect it to be much more effective."

On top of that, if it's been a while since your last COVID shot, you may not be as well protected. Immunity from the vaccine is optimal for about three months, Pekosz said, before it starts to go down.

"But if you get a COVID-19 vaccine now, you should be protected well through the fall," he added.

The Centers for Disease Control and Prevention advises getting a COVID-19 shot as soon as you're able, and getting a flu shot by the end of October while you're at it.