The US Centers for Disease Control and Prevention now calls the Delta variant of the novel coronavirus, also known as B.1.617.2, a “variant of concern.”

The variant of concern designation is given to strains of the virus that scientists believe are more transmissible or can cause more severe disease. Vaccines, treatments and tests that detect the virus may also be less effective against a variant of concern. Previously, the CDC had considered the Delta variant to be a variant of interest.