State health officials in South Carolina announced that they’ve identified two cases of the highly-contagious South African strain of coronavirus, marking the first cases in the United States, the Associated Press reports.

The people have had no known contact with one another, nor have they traveled out of the country recently, worrying public health officials about the unknown identity of Patient Zero in the United States.

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

The two patients are both adults but from different areas of the state:  one from the Low Country around Charleston and the other from Pee Dee region about 120 miles north.  They’ve had no known contact with one another.

The discovery of these cases reinforces the need to continue practicing personal health habits like wearing a mask and washing hands as ways of stopping the spread of the virus while vaccine distribution problems get resolved.

“While more COVID-19 vaccines are on the way, supplies are still limited. Every one of us must recommit to the fight by recognizing that we are all on the front lines now. We are all in this together,” Dr. Brannon Traxler, South Carolina Department of Health and Environmental Control Interim Public Health Director, said in a statement.