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Another coronavirus variant — different from the strain first detected in the United Kingdom — is being found more frequently across California, state officials said Sunday.

The L452R variant was identified in 12 California counties, including Los Angeles, Orange, Riverside, San Bernardino and San Diego.

This coronavirus variant has increasingly been detected in the state since November, and was identified in several large outbreaks in Santa Clara County, according to a California Department of Public Health news release.

“The fact that this variant was identified in several large outbreaks in our county is a red flag and must be investigated further,” Santa Clara County Health Officer Dr. Sara Cody said in a statement. “This virus continues to mutate and adapt, and we cannot let down our guard.”

This is not the same variant that health experts said could spread more easily after it was first found in the U.K. and later in several U.S. states, including California. This one, L452R, has been found in other countries and states, and health officials still don’t know if it’s more infectious.

“It’s too soon to know if this variant will spread more rapidly than others, but it certainly reinforces the need for all Californians to wear masks and reduce mixing with people outside their immediate households to help slow the spread of the virus,” said State Epidemiologist Dr. Erica Pan. “We also urge anyone who has been exposed to the virus to isolate from others to protect themselves and their loved ones.”

Pan said it’s not uncommon to find several variants of viruses. But it’s still unclear how widespread this variant is.

“Because genomic sequencing is not done equally across the state or country, it is too soon to know how prevalent the 452 variant is statewide, nationally or globally,” CDPH officials said.

Virologist Dr. Charles Chiu has been sequencing cases from multiple counties across the state over the past several months at University of California, San Francisco. He’s been increasingly finding L452R in coronavirus samples.

“It’s concerning that we have a variant that was actually pretty uncommon prior to early December that since then, is now roughly 25% of all the cases that we’re sequencing,” Chiu said in a news briefing Sunday.

At genomic sequencing labs, the new variant L452R went from being found in 3.8% of samples to about 25% within less than a month, according to Chiu.

“This variant carries three mutations, including L452R, in the spike protein, which the virus uses to attach to and enter cells, and is the target of the two vaccines that are currently available in the United States,” Chiu said. “Now that we know this variant is on the rise in our local communities, we are prioritizing it for study.”

Because the virus mutation is in the binding domain of the spike protein, there is a concern that it might have an effect on the effectiveness of the vaccine, Chiu said in a news briefing.

“The data so far is very preliminary but it basically does raise the concern that there may be some impact on the vaccine,” he added. “I think that’s the most uncomfortable saying — certainly much more work needs to be done in the laboratory.”

The L452R variant is not completely new. After it was first discovered in Denmark in March last year, the first case in California was found as early as May in Alameda County — though it remained “very rare” up until November, Chiu said.

It has also been found in Humboldt, Lake, Mono, Monterey, San Francisco and San Luis Obispo counties, as well as in several other states.