What to know about COVID-19 variants

Experts weigh in on what we know now about the delta variant and more.

The Centers for Disease Control and Prevention listed the COVID-19 delta variant as one of its “variants of concern” (VOCs) on June 15. According to the CDC, VOCs can be more contagious, more dangerous, less susceptible to available treatments or harder to detect. The uncontrolled spread of SARS-CoV-2, the virus that causes COVID-19, means the virus is mutating quickly. That’s why many new variants are being discovered in places with the highest infection rates and large numbers of unvaccinated individuals, like the United States, the United Kingdom, India and Brazil. “Viruses mutate; they change their form all the time,” said ABC News medical contributor, Dr. Simone Wildes, a board-certified infectious disease physician and public health expert at South Shore Health in Weymouth, Massachusetts. The World Health Organization (WHO) and the CDC are monitoring slightly different variants depending on whether the variant is a threat globally, or just in the United States. Just recently, for example, the WHO named a new variant called "mu" because it is spreading in some countries, but the CDC has not designated this variant because it is not considered a threat in the U.S.