The delta variant is a version of the coronavirus that has been found in 80 countries since it was first discovered in India. It got its name from the World Health Organization, which names important variants after letters of the Greek alphabet. Viruses always mutate, and most changes are not worrying. There is concern, however, that some variants might change enough to be more transmissible, make people sicker or avoid the protection of vaccines. Experts say the delta variant spreads more easily because of mutations that make it better at connecting to cells in our bodies. In the United Kingdom, the variant is now responsible for 90 percent of all new infections. In the U.S., it represents 20 percent of infections, doubling in the past two weeks. Health officials say it could become the country’s most common type as well. Dr. Anthony Fauci is the top disease expert in the U.S. “The delta variant is currently the greatest threat in the U.S. to our attempt to eliminate COVID-19,” he said.