B.1.429 was first discovered in July 2020 by researchers at the Cedars-Sinai Medical Center, California, in one of 1,230 virus samples collected in Los Angeles County since the start of the COVID-19 epidemic. It wasn't detected again until September when it reappeared among samples in California, but numbers remained very low until November. In November 2020, the CAL.20C variant accounted for 36 percent of samples collected at Cedars-Sinai Medical Center, and by January 2021, the CAL.20C variant was 50 percent of samples.