A new and highly contagious coronavirus variant first identified in South Africa has been found in the United States for the first time, with two cases diagnosed in South Carolina, state health officials said Thursday. The two cases don’t appear to be connected, nor do the people have a history of recent travel, the South Carolina Department of Health and Environmental Control said.

“That’s frightening,” because it means there are likely 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.”

The arrival of this variant now surging in other countries shows that “the fight against this deadly virus is far from over,” Dr. Brannon Traxler, interim public health director of the South Carolina agency, said in a statement. “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.”

The two people infected with this variant are both adults; one is from South Carolina’s Lowcountry and the other from the Pee Dee region, the state said, while withholding other information to protect their privacy.

Viruses are constantly mutating, with coronavirus variants circulating around the globe, but scientists are primarily concerned with the recent emergence of three of them. Other variants first detected in the United Kingdom and Brazil have also been confirmed in the U.S.  Researchers believe these three variants may spread more easily, and predicted it was only a matter of time before they appeared here.

“At this time, we have no evidence that infections by this variant cause more severe disease,” the U.S. Centers for Disease Control and Prevention said in a statement. “Like the UK and Brazilian variants, preliminary data suggests this variant may spread more easily and quickly than other variants.”

Also, scientists last week reported preliminary but troubling signs that some of the recent mutations may modestly reduce the strength of two current vaccines, although they stressed that the shots still protect against the disease. And there are signs that some of the new mutations may undermine tests for the virus and reduce the effectiveness of certain treatments.

The coronavirus has already sickened millions and killed more than 400,000 people in the United States.

While some European countries do extensive genetic testing to detect these variants, the U.S. has done very little of this detective work. But scientists have been quickly trying to do more, and they’re spotting these apparently more contagious variants as they do.

The Centers for Disease Control and Prevention has reported at least 315 cases of the U.K.-discovered variant in the United States. Those reports have come from at least 28 states, and health officials believe it could become the dominant strain in the U.S. by March. That variant has been reported in at least 70 countries.

The first U.S. case of the variant originally found in Brazil was announced earlier this week by health officials in Minnesota. It was a person who recently traveled to that South American nation. That version of the virus has popped up in more than a half-dozen countries.

The variant first found in South Africa was detected there in October. It since then has been found in at least 30 other countries.

Some tests suggest the South African and Brazilian variants may be less susceptible to antibody drugs or treatment with antibody-rich blood plasma from COVID-19 survivors, both of which help people fight off the virus.

Health officials also worry that if the virus changes enough, more people might get COVID-19 a second time.

President Biden on Monday reinstated COVID-19 travel restrictions on most non-U.S. citizens traveling from Brazil, the U.K. and South Africa. And the Centers for Disease Control and Prevention is recommending that Americans do not travel at this time.