Here’s What You Need to Know About the Multiple New Coronavirus Strains in the U.S.

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Editor’s Note: New details about these variants are emerging as researchers continue to learn more. While we aim to update this article as soon as new information becomes available, please check the CDC website for the latest details about variants in the United States.

On January 18, 2021, Los Angeles-based healthcare organization Cedars-Sinai released a statement detailing a new strain of the novel coronavirus, dubbed CAL.20C, that researchers believed may have been responsible for the marked surge in COVID-19 cases that subsequently took place across Southern California. By the middle of January, Los Angeles County had reported more than 14,000 COVID-19 deaths since the beginning of the coronavirus pandemic and over 1 million COVID-19 cases in that same time frame — with two-thirds of those cases occurring since November of 2020.

Cedars-Sinai researchers also found that CAL.20C was present in 36.4% of patients who tested positive for COVID-19 between November 22, 2020, and December 28, 2020 — and CAL.20C "was almost nonexistent in October" of that same year. The emergence of CAL.20C, which researchers believe originated in Southern California, may seem shocking. That’s not only because it appears to be spreading so rapidly, but also because it appeared at all.

CAL.20C is a variant — a virus that’s experienced mutations, which are changes to the virus’ structure that can alter how it functions — of SARS-CoV-2, the specific coronavirus that causes the disease COVID-19. Mutations can cause viral variants to behave differently than previous strains of the same virus. This may spark changes in everything from how the viruses are transmitted to the ways vaccines work against them, and these changes happen spontaneously as the virus spreads. That the resulting variants can also have unforeseen consequences is cause for concern during a pandemic that’s barely under control.

Another reason why CAL.20C feels so urgent? Aside from its rapid spread, it isn’t the only SARS-CoV-2 variant the United States is contending with. Others have emerged since the beginning of the pandemic, with several notable strains spreading rapidly during last several months. It’s still somewhat unclear exactly how these variants may impact our efforts to contain the virus — although scientists believe they may be responsible for numerous surges in COVID-19 cases across the country, despite growing numbers of vaccinated people. But research into them, which can better inform our pandemic response, is ongoing. With that in mind, here’s what we're learning about the variants spreading in the United States.