It was less than 1% of all new COVID-19 cases in mid-April, but the Delta variant accounts for nearly five in six cases, as of July 17.  An estimated 83% of new cases came from the more transmissible strain of the virus during the two weeks ending July 17.

The Alpha variant, previously the most prevalent strain since March, made up 8% of cases at the end of June.

The Delta variant has become prevalent since mid-May.

Centers for Disease Control and Prevention
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The concentration of the Delta variant varies by region. In New England, 38% of the cases are Delta-based, while in the four-state area of Iowa, Kansas, Missouri, and Nebraska, 87% of cases are Delta-based.

What are the characteristics of the most prevalent variants?

The CDC provides information on common COVID-19 variants. The federal government monitors genetic variations of the virus, classifying variants in three categories of increasing need for attention or action: variant of interest, variant of concern, and variant of high consequence. Designations may change with additional research. There are currently no existing variants of high consequence.

B.1.1.7 (Alpha): Considered a variant of concern, the Alpha variant was first detected in the United Kingdom and has a 50% higher transmission rate than older versions of the virus. The CDC says there is no impact on the effectiveness of antibody treatments and little impact on the efficacy of vaccines against the strain.

B.1.617.2 (Delta): The Delta variant is known for  being more transmissible  than older variants including the Alpha variant. It may impact the effectiveness of antibody treatments and vaccines. It is considered a variant of concern.

P.1 (Gamma): The variant was first identified in travelers from Brazil tested at an airport in Japan in early January. Certain types of antibody treatments are not as effective against the Gamma variant as opposed to other strains. It is considered a variant of concern.

B.1.526 (Iota): First identified in New York in November 2020, Iota is a variant of interest. Certain types of antibody treatments are less effective against the strain than earlier versions of the virus.

For more on COVID-19, visit the cases and deaths map or track state-level progress on vaccinations.

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