Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
To maximize protection from the Delta variant and prevent possibly spreading it to others, wear a mask indoors in public if you are in an area of substantial or high transmission.
UPDATE
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.

Variants and Genomic Surveillance for SARS-CoV-2

Variants and Genomic Surveillance for SARS-CoV-2
Updated Apr. 2, 2021
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Variant Proportions

Proportions of variants of concern and variants of interest in the US.
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Genomic Surveillance

What is a variant?

Viruses constantly change through mutation, and new variants of a virus are expected to occur over time.

About Variants of the Virus
Delta Variant

The Delta variant causes more infections and spreads faster than earlier forms of the virus that causes COVID-19. It might cause more severe illness than previous strains in unvaccinated people.

  • Vaccines continue to reduce a person’s risk of contracting the virus that cause COVID-19, including this variant.
  • Vaccines continue to be highly effective at preventing hospitalization and death, including against this variant.
  • Fully vaccinated people with breakthrough infections from this variant appear to be infectious for a shorter period.
  • Get vaccinated and wear masks indoors in public spaces to reduce the spread of this variant.

About the Delta VariantVariants in the US

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Variant Proportions in the U.S.

View data showing proportions of Variants of Concern and Variants of Interest.

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Global Variant Reports

View a global map showing reports of variants in each country.

Research and Selected Publications