California variant better able to evade vaccines, study suggests.

LOS ANGELES — A coronavirus variant that emerged in mid-2020 and surged to become the dominant strain in California doesn’t just spread more readily than its predecessors, it also evades antibodies generated by COVID-19 vaccines or prior infection and it’s associated with severe illness and death, researchers said.

In a study that helps explain the state’s dramatic surge in COVID-19 cases and deaths — and portends further trouble ahead — scientists at the University of California, San Francisco said that the cluster of mutations that characterizes the homegrown strain should mark it as a “variant of concern” on par with those from the United Kingdom, South Africa and Brazil.

“The devil is already here,” said Dr. Charles Chiu, who led the UCSF team of geneticists, epidemiologists, statisticians and other scientists in a wide-ranging analysis of the new variant, which they call B.1.427/B.1.429. “I wish it were different. But the science is the science.”

The new analysis is currently under review. It is expected to post late this week to MedRxiv, a website that allows new research to be shared before its formal publication.

Over five months starting on Sept. 1, the California strain, which is sometimes referred to as 20C/ L452R, rose from complete obscurity to account for more than 50 percent of all coronavirus samples that were subjected to genetic analysis in the state. Compared with strains that were most prominent here in early fall, the new strain seems to have an enhanced ability to spread, Chiu said.

Evidence suggests the variant is 19 percent to 24 percent more transmissible.

B.1.427/B.1.429’s genome includes three mutations that affect the crucial spike protein, which the virus uses to sneak into human cells and convert them into factories for its own production. One of those three mutations, dubbed L452R, affects the so-called receptor binding domain, helping the virus attach more firmly to target cells.

That adaptation has not been seen in coronavirus variants that have caused worry elsewhere.

In a UCSF lab, scientists also found that the L452R mutation alone made the California strain more damaging. A coronavirus engineered to have only that mutation was able to infect human lung tissue at least 40 percent more readily than were circulating variants that lacked the mutation. Compared with those so-called wild-type strains, the engineered virus was more than three times more infectious.

In the lab, the California strain also revealed itself to be more resistant to neutralizing antibodies generated in response to COVID-19 vaccines as well as by a previous coronavirus infection.

Compared with existing variants, the reduction in protection was “moderate … but significant,” the researchers said.

The coronavirus strain that’s now dominant in South Africa — and that has raised concerns about evading the immune system’s defenses — has been shown to reduce the effect of neutralizing antibodies by a factor of 6.2. With the California strain, the effect of these antibodies was reduced by a factor of two.

Dr. Marc Suchard, an expert on infectious disease tracking at UCLA, said that some of the team’s findings will probably be refined as more virus samples are genetically sequenced and more data come to light.

“It remains critically important that we actively sequence the virus as cases are diagnosed …,” said Suchard, who was not involved in the UCSF work.