The variant was first identified in India in December of 2020.
It was detected in the U.S. in March.
In some states where the vaccination rates are lower, the delta strain accounts for more than 80% of new infections, like in Iowa, Kansas, and Missouri, the CDC reports.
According to the World Health Organization, this strain is considered “the fastest and the fittest.”
Specialist Dr. Wilson told Yale Medicine delta is 50% more contagious.
“In a completely unmitigated environment—where no one is vaccinated or wearing masks—it’s estimated that the average person infected with the original coronavirus strain will infect 2.5 other people,” Dr. Wilson says. “In the same environment, Delta would spread from one person to maybe 3.5 or 4 other people.”
Health experts say the good news is that the vaccines being used in the U.S. are highly effective against the virus.
“We have two Americas: the vaccinated and the unvaccinated,” infectious disease specialist Dr. Paul Offit told NPR.
“We’re feeling pretty good right now because it’s the summer. But come winter, if we still have a significant percentage of the population that is unvaccinated, we’re going to see this virus surge again,” Offit says.