California coronavirus variant is spreading rapidly. Should we worry?

A COVID-19 vaccination site at Dodger Stadium in Los Angeles, California on February 11, 2021
A COVID-19 vaccination site at Dodger Stadium in Los Angeles, California on February 11, 2021. (Image credit: FREDERIC J. BROWN/AFP via Getty Images)

A variant of the new coronavirus that first appeared in Southern California last summer has now spread to more than a dozen U.S. states and several other countries, according to a new study.

The variant, known as CAL.20C, was first detected in a single case in Los Angeles County in July 2020, but it didn't show up again in Southern California until October 2020, according to the study, published Thursday (Feb. 11) in the journal JAMA. Then, cases of the variant skyrocketed in the L.A. area, coinciding with the region's winter surge in overall coronavirus cases. 

Now, CAL.20C accounts for nearly half of COVID-19 cases in Southern California and about a third of cases in the state based on an analysis of viral genomes posted to a global database called GISAID.

What's more, the researchers found that by the end of January, the variant had spread to 19 other states, up from five states in November 2020. It has also spread beyond the U.S. to six other countries — Australia, Denmark, Israel, New Zealand, Singapore and the United Kingdom.

The researchers suspect travelers from Southern California are spreading the variant elsewhere. "CAL.20C is moving, and we think it is Californians who are moving it," study co-senior author Jasmine Plummer, a research scientist at Cedars-Sinai Medical Center in Los Angeles, said in a statement.

The CAL.20C variant — also known as B.1.429 — is defined by five distinct mutations, three of which are in the virus's spike protein, the structure that allows the virus to bind to and infect human cells.

Despite the variant's apparent rise in Southern California, scientists still don't know if CAL.20C is more contagious than other coronavirus strains. The variant may have become more common simply by chance, rather than having an inherent biological advantage, according to The New York Times.

The researchers also noted that their study analysis was limited to samples included in publicly available databases as well as about 2,300 samples from their hospital, and they cannot rule out "collection bias," meaning samples may have been collected from certain populations but not others.

However, the variant has a concerning mutation known as L452R. This genetic mutation is in a gene that encodes for the so-called receptor-binding domain (RBD), a spot on the spike protein where the virus first docks with human cells. Mutations in this area could in theory allow the virus to spread more easily, Live Science previously reported.

Last month, California health officials said they were concerned about a variant with the L452R mutation because it had been identified in several large outbreaks in Santa Clara County, Live Science previously reported.

The Cedars-Sinai researchers are continuing to study CAL.20C to determine if it is more contagious, more severe or better able to resist current vaccines, compared with other strains.

Originally published on Live Science.  

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.