Viruses often undergo genetic changes or mutations over time, leading to new versions or variants of a virus. Multiple variants of the COVID-19 virus that appear to spread more easily and could cause more severe cases have been identified worldwide including in the U.S. including the Delta variant. The CDC has reported that recent data has shown that it is possible for fully vaccinated people to transmit the Delta variant to others. The CDC reports that the Delta variant causes more infections and spreads faster than early forms of the COVID-19 virus. The CDC recommends that fully vaccinated people wear masks in public indoors in locations with a substantial or high number of people infected with COVID-19. The CDC COVID-19 Data Tracker is a tool to determine the level of COVID-19 transmission throughout the U.S.
Scientists and doctors are studying the new variants to understand how they spread from person to person, cause  illness, how well current COVID-19 tests detect them, and the efficacy of current COVID-19 treatments and vaccines for these variants. Research continues to show that the current COVID-19 vaccines are effective in reducing serious illness, hospitalization and death caused by these variants.
For the most up to date information on COVID-19 virus variants, visit the CDC website.