COVID-19 (Coronavirus)
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Coronavirus Strains: What You Need to Know

New variants of the COVID-19 virus.
Eric Vail, MD

Eric Vail, MD

Cedars-Sinai researchers recently discovered a unique strain of SARS-CoV-2, the virus that causes COVID-19. Dubbed CAL.20C—and also known as B.1.429—this strain originated in Southern California. Researchers detected CAL.20C in more than one-third of cases in their study of Southern California patients between November and December 2020. It is now spreading across the country—traveling with people as they visit other states.

Like all viruses do, SARS-CoV-2 is evolving. The more any virus spreads, the more likely it is to undergo tiny changes to its genes—the result is called a variant.

A consistent group of variants that are found in clusters of infections creates a new strain, like the SARS-CoV-2 strains identified in the United Kingdom, Brazil and South Africa. New strains can help any virus spread more easily and cause more severe effects—though spreading the same way and causing the same disease.

We spoke with Cedars-Sinai experts Dr. Eric Vail, Cedars-Sinai's director of Molecular Pathology, whose lab recently identified CAL.20C, and Dr. Michael Ben-Aderet, Cedars-Sinai's associate medical director of Hospital Epidemiology, about what you need to know about new strains of the virus that causes COVID-19.



Michael A. Ben-Aderet, MD

Michael A. Ben-Aderet, MD

How many new strains of SARS-CoV-2 are there?

It's hard to tell. Scientists around the world have detected tens of thousands of variants. We don't know which variants will become dominant and spread broadly. We do know that SARS-CoV-2 is not evolving as quickly as other viruses, such as influenza, and the changes are normal.

"It isn't completely unexpected," Dr. Ben-Aderet says. "Variants are very common—what's important to understand is that these different strains aren't transmitted in different ways. The molecular changes make them potentially more infectious—but the mechanism of transmission from person to person is exactly the same."

Do the new strains spread more easily?

There is some evidence to suggest that some strains are more infectious—meaning it could take less exposure to infect you.

The Southern California strain, CAL.20C, may be more easily transmissible—but it's also possible the strain is so prevalent mainly because there was so much community spread during the winter holidays. So Dr. Vail's team is studying two possibilities: whether the strain caused the winter surge in Southern California because it is spread more easily, or whether the new strain evolved because of increased transmission—because the level of the virus in the community is so high.

"We're looking at the fact that we saw CAL.20C become more prevalent over time, which coincided with our surge in cases," Dr. Vail says.

Are the new strains deadlier, or do they make people sicker?

While there are early reports that suggest that some strains may cause more severe disease, the data is still preliminary. There's currently no peer-reviewed evidence to suggest that any of the identified strains cause more severe illness or can cause death more easily.



Does the COVID-19 vaccine protect against new strains?

All COVID-19 vaccines available in the United States have been shown to be highly effective at preventing COVID-19, and even more effective at preventing severe illness from COVID-19.

Some studies of antibody protection after vaccination have found differences in antibody response to different strains. However, the body's immune response is highly complex, and there is no scientific evidence that the vaccines are not effective in preventing disease. Experts continue to study the effect of vaccination on severity of illness from COVID-19, as well as its impact on transmission of the virus from person to person.


"The most important thing is to abide by all the advice together: wear a mask, don't gather, wash your hands and get the vaccine when you can."


When a person tests positive for the virus that causes COVID-19, will they know which strain infected them?

No. While this information is relevant to researchers who study the disease so they can track the spread and possibly tailor clinical recommendations, there is no benefit for patients to know which strain they have contracted.

Does infection with one strain lead to immunity from other strains?

Yes. Though research is ongoing, it seems likely that if you get infected with one strain, you will be protected from another.

"Your body's immunity has many layers, and you generally develop protection from the virus with a complex response, including antibodies, which is broad enough to cover the known strains," says Dr. Ben-Aderet.



Will the vaccine stop the virus from developing new strains?

The best way to stop the virus from changing is to stop the spread in general. Ideally, as more people are vaccinated and fewer people are infected, the virus won't have the option to evolve as easily.

"If there is less virus in circulation, and less transmission, it breaks the cycle," says Dr. Ben-Aderet. "By lowering community rates, the virus will have less opportunity to replicate, spread and change."

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