Variants of SARS-CoV-2

When a virus develops a new mutation, it is called a variant of the original virus.

As viruses spread, they constantly change through mutations to their genetic code. Most mutations in the SARS-CoV-2 genome do not affect the functioning of the virus. However, mutations in the spike protein of SARS-CoV-2, which binds to receptors on cells lining the inside of the human nose, may make the virus easier to spread or affect how well vaccines protect people. Other mutations may lead to SARS-CoV-2 being less responsive to treatments for COVID-19.

The Centers for Disease Control and Prevention (CDC) classifies a variant of concern as a variant with 1 or more mutations that allow the virus to infect people more easily or spread from person to person more easily, make the virus less responsive to treatments, or affect how well vaccines work against the virus.

The CDC defines a variant of high consequence as one for which there is clear evidence that “prevention measures or medical countermeasures have significantly reduced effectiveness relative to previously circulating variants,” such as current vaccines, treatments, or testing being less effective, resulting in more severe disease and increased hospitalizations. Currently, no variants of high consequence have been identified worldwide.

Alpha (B.1.1.7) was the first identified major variant of concern. It was first identified in the United Kingdom in the fall of 2020 and spreads approximately 50% better than the original SARS-CoV-2. There is some evidence that the Alpha variant may cause more severe disease. Current SARS-CoV-2 vaccines and monoclonal antibody therapies appear to be effective against the Alpha variant.

The variants Beta (B.1.351), first identified in South Africa, and Gamma (P.1), first identified in Brazil, both exhibit increased transmissibility, but not as much as the Alpha variant. Some of the current monoclonal antibodies are less effective against the Beta and Gamma variants. Both Beta and Gamma variants are less well neutralized by antibodies in vaccinated individuals, and there is a small decrease in the effectiveness of currently available vaccines against these 2 variants.

Delta (B.1.617.2) is currently the most prevalent variant in the United States. Early data suggest that the Delta variant spreads almost twice as quickly as the original SARS-CoV-2 virus. It is not yet clear whether Delta causes more severe disease. The Delta variant may not be neutralized as well by antibodies in vaccinated people. Early data suggest a small decrease in vaccine effectiveness in patients who are fully vaccinated against SARS-CoV-2. However, individuals who have received only a single dose of a 2-dose vaccine regimen are much less protected against the Delta variant. People who have not received a COVID-19 vaccine are at high risk of becoming infected with the Delta variant because of its increased transmissibility.

Surveillance programs will continue to monitor for SARS-CoV-2 variants and the possible implications of these variants for disease spread, treatments, and vaccines. Vaccination is safe and remains the most effective way to prevent severe disease and limit spread of SARS-CoV-2.

Published Online: August 13, 2021. doi:10.1001/jama.2021.14181

Conflict of Interest Disclosures: Dr Lauring reported receiving personal fees from Sanofi and Roche. No other disclosures were reported.

Source: Centers for Disease Control and Prevention