On June 15, 2021, CDC announced reclassification of the SARS-CoV-2 variant B.1.617.2 (Delta) as a variant of concern (VOC). This variant was initially identified in India in December 2020 and was initially classified as a variant of interest (VOI). The B.1.617.2 (Delta) lineage has been detected in at least 66 countries, including the United States.
SARS-CoV-2 variants can be categorized into the following three classes based on a Variant Classification scheme developed by a US government interagency group:
A variant of concern might require one or more appropriate public health actions, including
- Notification to the World Health Organization (WHO)
- Increased testing
- Local or regional efforts to control spread
- Research to determine the effectiveness of existing tests, vaccines, and treatments against the virus
In the United States, for the two-week period ending May 22, 2021, the proportion of cases attributed to B.1.617.2 (Delta) is estimated to be 2.7%, and CDC nowcast data predict that the proportion of B.1.617.2 will increase to 9.9% for the two-week period ending June 5, 2021.
While further U.S. studies are needed, initial evidence suggests that the B.1.617.2 (Delta) is more transmissible compared with other variants, including B.1.1.7 (Alpha). There is preliminary data to indicate B.1.617.2 may be less susceptible to neutralizing antibodies in laboratory studies; importantly, however, vaccines authorized for use in the United States have been reported to be effective against B.1.617.2 as well as other variants.
CDC, in coordination with the SARS-CoV-2 Interagency Group, will continue to monitor B.1.617.2 (Delta) as well as other VOIs and VOCs to see if they have any impact on SARS-CoV-2 transmission, disease severity, and effectiveness of existing tests, vaccines, and treatments.