Data from the Centers for Disease Control (CDC) shows that the variant, which originated in India, has infected people at an uncomfortable rate over the past few weeks.
On May 22, the variant accounted for only about 2.7% of cases, but as of last week it is now closer to 10% of all cases in the U.S., according to the CDC.
However, the rate was already higher in some parts of the country with Missouri recording the variant as roughly 6.8% of cases in the state as of May 22. Kansas and other states with high rural populations have measured high rates of community spread over the past two weeks.
The Midwest and Mountain West states including Iowa, Kansas, Missouri, and Nebraska are recording a rate closer to 23.5% of all cases resulting from the Delta strain.
Around 8% of counties in the U.S. have recorded a high level of transmission, with around half of the counties in the U.S. still showing a moderate level of transmission.
Kansas, meanwhile, has closer to the national average with around 10% of cases from the Delta variant, ABC News reported.
The variant was first detected in October and the CDC upgraded the variant from one "of interest" to one "of concern."
"It shows us that what we've got in the community is a much more infectious variant that we are having to deal with, which shows why we have such an explosion of cases not just in Greene County, but in southwest Missouri," Kendra Findley, administrator of community health and epidemiology with Green County, told the St. Louis Post-Dispatch.
Health officials have repeated warnings that the Delta strain is likely to become the dominant strain in the U.S. within the next few weeks as the rate appears to be on track to continue doubling week over week.
"Right now in the U.S., it’s about 10% of infections doubling every two weeks, so it’s probably going to become the dominant strain here in the U.S.," Dr. Scott Gottlieb, former head of the FDA, said on CBS’s "Face the Nation" last week.
"That doesn’t mean we’re going to see a sharp uptick in infections but it does mean that this is going to take over and I think the risk is really to the fall that this could spike a new epidemic heading into the fall," he added.
However, health officials maintain that the current vaccines are still highly effective against the variant. Efficacy against the Delta variant appears to be around 88% - lower than the 95% that vaccines displayed against older variants, but still far more effective than the average flu vaccine by almost double.
The Midwest states, though, have shown a sluggish administration of vaccine doses, with most states seeing under half of their population fully vaccinated at this point in time, according to Our World in Data.
The CDC lists the Alpha, Beta, Epsilon, and Gamma variants as being "of concern," while the Eta, Iota, Kappa, Delta, and Zeta remain variants of interest.