On June 22, 2021, the Indian government categorized Delta Plus (also known as B.1.617.2.1 or AY.1) as an official Variant of Concern (VOC) of the virus that causes COVID-19.

Delta Plus, which was first identified in India, has also been detected in other countries around the world, including the U.S., the U.K., China, Japan, Nepal, Russia, Portugal, Switzerland, and Poland. The Delta Plus variant is related to the Delta variant (also known as B.1.617.2), which is an existing Variant of Concern and is thought to be behind India's massive second wave of infections in April and May of 2021.

The Delta Plus variant has mutations that are similar to the Delta variant. It has an additional mutation called K417, which is also found in the Beta variant that was linked to high hospitalization rates and the Gamma variant that was linked to high transmission rates.

Research is still underway to understand Delta Plus. The Indian health ministry has said that initial studies suggest this variant can spread more easily, bind more easily to lung cells, and potentially be more resistant to monoclonal antibody therapy (see this Health Desk explainer for more information.)).

Some scientists question whether there is sufficient data at this time to indicate that the Delta Plus variant is more dangerous than the Delta variant. Typically, researchers study several hundreds of patients sick with a variant to find out whether they are at greater risk of disease. There were under 200 examples of Delta Plus on the global open sharing database GISAID at the time of India's announcement of the new Variant of Concern.

Since the Delta variant is already a Variant of Concern, it may not be unusual for Delta plus to be labeled a VOC as well since "all lineages of the Delta variant are Variants of Concern," according to a scientist of one of the 28 Indian labs involved in genome sequencing. This announcement on the Delta Plus variant may be part of a precautionary approach taken by the Indian government, in the wake of the deadly rise in cases related to the spread of the Delta variant.

The announcement of the Delta Plus variant comes after the Indian healthcare system was overwhelmed by a deadly second wave of infections, where the Delta variant was thought to play a major role.

The highly transmissible Delta variant has spread to at least 77 countries and regions and currently makes up over 20% of all COVID-19 cases in the U.S. Initial studies suggest the Delta variant could be 40-60% more transmissible than the Alpha variant (also known as B.1.1.7) first identified in the U.K., which was already thought to be 50% more transmissible than the original strain of the novel coronavirus first identified in China.

The director of the U.S. Centers for Disease Control and Prevention (CDC) said that the Delta Plus variant could become one of the dominant strains in the U.S. As a precautionary measure, some regional officials have started updating mask guidance to include voluntary masking indoors regardless of vaccination status.