The mutated version of the virus, first identified in South Africa, was found in two cases in South Carolina. Public health officials said it’s almost certain that there are more infections that have not been identified yet. They are also concerned that this version spreads more easily and that vaccines could be less effective against it.

The two cases were discovered in adults in different regions of the state and do not appear to be connected. Neither of the people infected has traveled recently, the South Carolina Department of Health and Environmental Control said Thursday.

“That’s frightening,” because it means there could be more undetected cases within the state, said Dr. Krutika Kuppalli, an infectious diseases physician at the Medical University of South Carolina in Charleston. “It’s probably more widespread.”