The US Centers for Disease Control and Prevention is now calling 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.

What we know: The CDC said the Delta variant, which was first identified in India, shows increased transmissibility, potential reduction in neutralization by some monoclonal antibody treatments under emergency authorization and potential reduction in neutralization from sera after vaccination in lab tests.

The World Health Organization classified the Delta variant as a variant of concern on May 10.

Covid-19 cases have been declining over the past few months in the United States, but there’s concern that could change as the pace of vaccinations slows and the Delta variant spreads.

Read more about the Delta variant here.