Inactivated SARS-CoV-2 Variant Delta, Lineage B.1.617.2 (USA/PHC658/2021)

Like other RNA viruses, SARS-CoV-2 will continue to mutate and new variants will emerge as long as it circulates. If a variant provides a selective advantage to the virus, it will become more prevalent. The U.S. Department of Health and Human Services established an interagency task force on SARS-CoV-2 and created a classification system that includes "variants of concern," "variants of concern," and "variants of high consequence." The B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma), and B.1.617.2 (Delta) variants are all considered "variants of concern"—those with one or more mutations that make the virus more transmissible, reduce its responsiveness to treatment, or affect vaccine effectiveness.

The Delta variant was first identified in India in December 2020 and quickly spread throughout the largely unvaccinated country, resulting in a significant number of cases, hospitalizations, and deaths. In the United Kingdom, the Delta variant also spread rapidly despite high vaccination coverage, though hospitalizations and deaths increased at a much slower rate. Some public health experts speculate that this rapid spread is at least partially due to the country''s decision to delay second doses of the vaccine. In the United States, the Delta variant was first identified in March 2021. Since then, Delta has become the dominant variant in the country, triggering a new wave of infections. The Delta variant is highly transmissible, estimated to be approximately 60% more transmissible than the Alpha variant, and the CDC indicates that its basic reproduction rate (R0; the estimated number of secondary infections transmitted from an infected person to susceptible people) is between 5 and 8.