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You may have read about new coronavirus variants spreading around the country. But what is a variant, and where does it come from? Here are the basics, based on information from the American Medical Association, the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO).

What are variants and subvariants?

Viruses mutate, or change, over time. The result is new versions, or variants, of that virus. Different variants can work differently. For example, the Omicron variant of the coronavirus spreads more easily than some others. Subvariants happen when an existing variant mutates again, but the change is not big enough to classify as a new variant.

Are new variants always more dangerous?

Not always. Some variants can cause more severe illness. Others are less dangerous.

Will there always be new coronavirus variants?

Scientists expect new variants to emerge from time to time. Some may go away quickly, while others may stick around.

How can we help slow down new variants?

Viruses mutate as they spread, so the best way to slow down variants is to slow the spread:

• Stay up-to-date with your COVID-19 vaccines and boosters.
• If you think you may be sick, take a COVID-19 test.
• Wear a mask when recommended.

What is a "variant of concern?"

CDC and the WHO track new variants. Sometimes a new variant may be more dangerous than previous ones. That might be because compared to other variants:

• It is more likely to make people very sick.
• Tests do not detect it as well.
• Vaccines and past infections do not protect people as well.
• It is more contagious than other variants.

If at least one of those is true, CDC may call the new variant a "variant of concern." For example, the Delta variant was considered a variant of concern because it caused more severe illness in many people. The Omicron variant is not as likely to cause severe illness, but it is very contagious.

The WHO also calls some new strains of the coronavirus "variants of concern." What's the difference? The WHO tracks which variants are dangerous around the world. CDC focuses on how the variant affects people in the U.S.

Do COVID-19 vaccines still work against new variants?

So far, all available vaccines offer protection against variants of COVID-19. But vaccine protection can fade over time. Stay protected by following CDC's guidelines on when to get your next booster.

For more information on COVID-19, visit our Coronavirus health topic center.

Reviewed 2/28/2023