Two coronavirus variants first discovered in California have advanced to “variants of concern,” according to the Centers for Disease Control and Prevention.

The agency updated its website Tuesday, adding that the new versions — called B.1.427 and B.1.429 — are more contagious, more capable of evading some COVID-19 therapies, and moderately more resistant to antibodies from both natural infection and vaccination than the original coronavirus strain.

Although concerning, scientists say the virus is doing what it can to survive, and that means regularly changing through mutations, producing new — and expected — variants along the way. Whereas some “emerge and disappear,” others “emerge and persist.”

The increased concern doesn’t mean preventive measures such as hand-washing, physical distancing and mask wearing, as well as COVID-19 vaccines, are no longer fit to protect us, experts say. However, more research is needed to understand how much the vaccines’ effectiveness decreases when put up against the variants from California, and if that decrease matters.

“If we can get enough people vaccinated, we will be able to deal with these variants simply because we won’t have ongoing transmission,” Dr. Charles Chiu, an infectious diseases physician at the University of California, San Francisco, told The New York Times.

Still, the variants first discovered in California are less of a concern compared to those that emerged from the U.K. and South Africa, which studies show are 50% more transmissible. The variant from California is 20% more transmissible.

Chiu is the senior author of a non-peer reviewed study posted last week that found the variants from California first emerged around May 2020, making up over 50% of coronavirus cases sequenced by scientists in the state from Sept. 1, 2020, to Jan. 29, 2021.

This translates to an 18% to 24% jump in transmissibility compared to other circulating coronavirus strains, the study says.

The researchers found the variants had two times the viral load — the total amount of virus a person has inside them — than other coronavirus strains and showed a 4- to 6.7-fold decrease in antibodies in recovering COVID-19 patients. Among vaccinated individuals, antibody levels dropped two-fold.

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What does ‘variant of concern’ mean?

The CDC says a “variant of concern” is one “for which there is evidence of an increase in transmissibility, more severe disease (increased hospitalizations or deaths), significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures.”

It’s one step higher from a “variant of interest,” which includes some of the same attributes, but differs mostly in that the concerns are based on associations, not evidence. Current variants of interest include two that were discovered in New York, called B.1.526 and B.1.525, as well as one found in Brazil called P.2.

Other variants of concern include B.1.1.7 from the U.K., P.1 from Japan/Brazil and B.1.351 from South Africa, in addition to the the two from California.

Although evidence shows the variants of concern are more contagious and could partially evade COVID-19 therapies and antibodies, they are not yet considered variants “of high consequence.”

These types of variants have “clear evidence that prevention measures or medical countermeasures have significantly reduced effectiveness relative to previously circulating variants,” the CDC says. This means the variants would have the power to significantly evade vaccine effectiveness, resulting in a large number of people getting infected after vaccination or developing severe disease, which the vaccines currently prevent.

No coronavirus variants in the U.S. are of this much concern, the CDC notes.

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