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A coronavirus variant first detected in Los Angeles County last year has spread to at least 19 states and is now showing up in 44% of new cases tested in Southern California, Cedars-Sinai researchers announced Thursday.

The variant, dubbed CAL.20C, has spread quickly throughout the region in recent months and researchers believe travelers from California carried it to other states and abroad to six other countries, according to a study published in the Journal of the American Medical Association.

It’s still not clear whether the Southern California variant is deadlier or more infectious than current coronavirus strains, and researchers are still trying to determine whether it would resist vaccines.

It was first found in one case in L.A. County in July last year, but it didn’t reemerge in the region again until October. By November and December, it was spreading quickly around the country amid the rapid surge in infections, hospitalizations and deaths.

Now, the strain has been found in nearly half of coronavirus samples collected and checked for mutations in the Southern California region this January, and 35% of samples from throughout California.

That’s double the percentage found in samples that underwent next-generation sequencing the previous month, Cedars-Sinai said in a news release.

“CAL.20C is moving, and we think it is Californians who are moving it,” Cedars-Sinai research scientist Jasmine Plummer said.

This variant is different from the United Kingdom and South African strains, which have both been detected in California.

“New variants do not always affect the behavior of a virus in the body,” said Dr. Eric Vail, one of the study’s authors. “But we are interested in the CAL.20C strain because three of its five variants involve the so-called spike protein, which enables the SARS-CoV-2 virus to invade and infect normal cells.”

The variant has three mutations in its spike protein, the part of the virus that attaches to human cells. That includes the L452R mutation which has been found in several large coronavirus outbreaks in Santa Clara County.

The Southern California variant, CAL.20C, has also been detected in the states of Alaska, Arizona, Connecticut, Georgia, Hawaii, Maryland, Michigan, New Mexico, Nevada, New York, Oregon, Rhode Island, South Carolina, Texas, Utah, Washington, Wisconsin, Wyoming and in Washington, D.C.

Abroad, it was found in Australia, Denmark, Israel, New Zealand, Singapore and the United Kingdom.

With COVID-19 vaccinations still moving slowly across the country, the emergence and spread of mutated virus has raised alarms and prompted calls from local health officials to limit travel.

California Gov. Gavin Newsom earlier this week said there have been more than 1,200 cases of two different kinds of “West Coast variants.”

In L.A. County, officials have announced finding eight cases of the U.K. variant, B.1.1.7, which the Centers for Disease Control and Prevention said could become dominant across the U.S. by March. 

L.A. County Health Director Barbara Ferrer said that though it’s unlikely L.A. County’s latest surge was due to the U.K. variant, it’s possible there were mutations that were circulating that could have been slightly more infectious.

“There’s no way that we don’t have a fair amount of variants circulating,” she said. “It’s just a question of how much and does it become dominant.”