Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission.
UPDATE
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.

What is Genomic Surveillance?

What is Genomic Surveillance?

Viruses are constantly changing, and this includes SARS-CoV-2, the virus that causes COVID-19. These genetic variations occur over time and can lead to the emergence of new variants that may have different characteristics.

The SARS-CoV-2 genome encodes instructions organized into sections, called genes, to build the virus. Scientists use a process called genomic sequencing to decode the genes and learn more about the virus. Genomic sequencing allows scientists to identify SARS-CoV-2 and monitor how it changes over time into new variants, understand how these changes affect the characteristics of the virus, and use this information to better understand how it might impact health.

For example, some variant viruses are of particular concern because they spread more easily, cause more severe disease, or may escape the body’s immune response.

As CDC and public health partners sequence more SARS-CoV-2 genomes, we will improve our understanding of which variants are circulating in the US, how quickly variants emerge, and which variants are the most important to characterize and track in terms of health.

Us Variant
US COVID-19 Cases Caused by Variants

View a map showing the number of confirmed cases in each state.

Global Variant Reports

View a global map showing reports of variants in each country.

SARS-CoV-2 genome

Genes in the SARS-CoV-2 genome that contain instructions to build parts of the virus are shown in different colors. For example, the brown section in the picture has genetic instructions to build the spike protein, which then allows the virus to attach to human cells during infection. This section of the genome serves as a key region for monitoring mutations.

How do variants occur?

genome-envelope

The virus genome is packed inside an envelope that contains proteins, including the spike protein.

Mutations are changes in the genetic code of a virus that naturally occur over time when an animal or person is infected. While a certain amount of genetic variation is expected to occur as SARS-CoV-2 spreads, it’s important to monitor circulating viruses for key mutation(s) that happen in important regions of the genome. Many mutations do not affect the virus’s ability to spread or cause disease because they do not alter the major proteins involved in infection; eventually these are outcompeted by variants with mutations that are more beneficial for the virus.

To find more information about the mutations and variants CDC is monitoring in the US and globally, go to the SARS-CoV-2 Variants page.

How do variants occur?

Mutations are changes in the genetic code of a virus that naturally occur over time when an animal or person is infected. While a certain amount of genetic variation is expected to occur as SARS-CoV-2 spreads, it’s important to monitor circulating viruses for key mutation(s) that happen in important regions of the genome. Many mutations do not affect the virus’s ability to spread or cause disease because they do not alter the major proteins involved in infection; eventually these are outcompeted by variants with mutations that are more beneficial for the virus.

To find more information about the mutations and variants CDC is monitoring in the US and globally, go to the SARS-CoV-2 Variant page.

genome-envelope

The virus genome is packed inside an envelope that contains proteins, including the Spike protein.