Variants of SARS-CoV-2, the virus that causes COVID-19, are expected to continue to emerge.

Some variants will emerge and disappear, and others will emerge and continue to spread and may replace previous variants. For example, the variant of the virus that caused the first U.S. COVID-19 cases in January 2020 is no longer detected among variants circulating in the country.

CDC’s national SARS-CoV-2 genomic surveillance program identifies and tracks SARS-CoV-2 variants circulating in the United States and calculates the proportion of variants causing infections. Estimates will be updated every Tuesday.