SARS-CoV-2, the virus that causes COVID-19, is constantly changing and new variants of the virus are expected to occur. Sometimes new variants emerge and disappear. Other times, new variants persist. Numerous variants of the virus that causes COVID-19 are being tracked in the United States and globally during this pandemic. As the virus spreads, it has new opportunities to change and may become more difficult to stop. These changes can be monitored by comparing differences in physical traits (such as resistance to treatment) or changes in genetic code (mutations) from one variant to another. By studying each variant and understanding these differences, scientists can monitor, and often predict, whether a variant is more dangerous than others. Scientists can also use this information to track the spread of a variant.

CDC is using multiple data collection systems to monitor variants in the United States. Each system plays an important role in effectively understanding the emergence of new variants, how variants are entering and spreading in the United States, and which variants are most prevalent within U.S. communities. This page summarizes three different systems being used, including the 1) National SARS-CoV-2 Genomic Surveillance System, the 2) National Wastewater Surveillance System, and the 3) Traveler-based SARS-CoV-2 Genomic Surveillance Program.

As demonstrated on this page, SARS-CoV-2 variants are tracked using complementary surveillance systems. As the data collection processes vary in the systems summarized, variants identified in the systems also may vary. For example,

• National SARS-CoV-2 Genomic Surveillance System sequences a nationally representative selection of clinical respiratory specimens to identify and monitor the spread of variants.

• National Wastewater Surveillance System works with health departments, laboratories, and wastewater utilities to collect and provide information on SARS-CoV-2 infection levels in participating communities.

• Traveler-based SARS-CoV-2 Genomic Surveillance Program collects clinical specimens from travelers arriving at several major international airports in the United States for early detection of variants entering the country and to fill gaps in global surveillance.