A study by researchers at Cedars-Sinai indicates there is a unique strain of COVID-19 causing many of the local infections. (photo by Edwin Folven)

Cedars-Sinai Medical Center has reported that a new strain of the coronavirus has been found in more than one-third of COVID-19 cases in Los Angeles, and may be contributing to the surge in cases across Southern California, according to new research.

The strain, which the investigators designated as CAL.20C, is believed to be in part responsible for the dramatic increase in cases over the last two months. The Cedars-Sinai findings did not indicate whether the strain is more deadly than other current forms of the coronavirus.

CAL.20C is distinct from another virus mutation identified in Britain – known as B.1.1.7 – that is also spreading in the United States and is believed to be highly transmissible. In Southern California, B.1.1.7 has been found in scattered coronavirus cases in Los Angeles, San Diego and San Bernardino counties. In contrast, the CAL.20C strain was identified in 36.4% of cases in the Cedars-Sinai study.

CAL.20C includes a virus variant that the California Department of Public Health reported on Jan. 17 based on data submitted by Cedars-Sinai and other investigators. This variant, dubbed L452R, is one of five recurring mutations that constitute the CAL.20C strain, which is propagating across the country, starting in Los Angeles.

“The recent surge in COVID-19 positive cases in Southern California coincides with the emergence of CAL.20C,” said Eric Vail, assistant professor of pathology and director of molecular pathology in the Department of Pathology and Laboratory Medicine at Cedars-Sinai. Vail is the co-corresponding author of the study, submitted to medrxiv.org, an online archive for health science manuscripts that are not yet peer-reviewed, while simultaneously submitted for peer-review on Jan 14.

Los Angeles County has emerged as one of the nation’s COVID-19 hotspots. From the start of the pandemic through mid-January, the county has reported more than 1 million COVID-19 cases and nearly 14,000 deaths. More than two-thirds of the cases were added since the beginning of November.

The emergence of the newly-detected strain coincides with a period at or before the onset of the current spike in Southern California. Of further concern, the investigators, using publicly available databases, have detected the CAL.20C strain in multiple recent patient samples in Northern California, New York, Washington, D.C., and abroad.

While the CAL.20C strain was almost nonexistent in October, by December, 36.4% of virus samples from Cedars-Sinai patients were determined to be the strain, as were 24% of all samples from Southern California.

“The double-digit prevalence of the CAL.20C strain in November and December was striking given that it was first observed in July 2020 in just one of 1,230 virus samples in Los Angeles County and had not again been detected in Southern California until October,” said Jasmine Plummer, research scientist at the Cedars-Sinai Center for Bioinformatics and Functional Genomics, and a co-corresponding author of the study.

Wenjuan Zhang, assistant professor in the Department of Pathology and Laboratory Medicine at Cedars-Sinai and first author on this study, said the research team is, “not sure what the new findings mean in terms of the infectivity and antibody resistance of the CAL.20C strain, which is important for follow-up studies that will need to be completed.”

For information, visit cedars-sinai.org.