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The Mu variant: 5 things to know

Illustration of a coronavirus.

Oct. 8, 2021—If you've read news reports about the emergence of the Mu variant of the coronavirus, you might wonder how concerned you need to be. Just what is this coronavirus strain—and is it a potential concern here in the U.S.? Here are some answers to those questions:

Q. What is the Mu variant?

A. Like all viruses, the coronavirus changes over time through genetic mutations. This results in new virus strains, or variants. The Mu variant, also known as B.1.621, is one such strain. It first appeared in Colombia in January 2021 and has spread around the world. As of October 2021, nearly 5,000 cases of the Mu variant had been counted in the U.S.

Q. Is it on the rise in the U.S.?

A. No. Unlike the Delta variant, which now makes up more than 99% of all U.S. COVID-19 cases, the Mu variant has been slow to gain a foothold here. But the Centers for Disease Control and Prevention (CDC) continues to closely monitor the Mu variant and other emerging strains.

Q. Could it become as bad as the Delta variant?

A. The rise of the Delta variant led to a surge in COVID-19 cases. Delta spreads faster and more easily than previous strains, and it can cause more severe illness. By contrast, the Mu variant does not appear to pose an immediate threat in the U.S., according to CDC. The situation could change, but for now, Mu doesn't appear to be the next Delta.

Q. Is it resistant to COVID-19 vaccines?

A. No. Some scientists have expressed concern that COVID-19 vaccines might be less effective against the Mu variant because of mutations to the spike protein on the surface of the virus. (That spike protein is what the vaccines target.) But there's no evidence yet to suggest that's the case. The vaccines continue to protect against all current coronavirus strains, including Mu.

Q. Is there anything special I should do to protect myself?

A. You should keep taking precautions to avoid COVID-19. That includes getting vaccinated as soon as you can and continuing to wear a mask when appropriate. These measures help keep you safe. Plus, they may also help to prevent future variants from emerging. That's because slowing the spread of the virus gives it fewer chances to mutate into a new strain.

Check out our Coronavirus health topic center for more COVID-19 updates.

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