BOSTON (CBS/AP) – A new Covid variant that was first detected in South Africa is raising new concerns around the world. The discovery of the variant, named Omicron by the World Health Organization, has caused nations to stop air travel from there as stocks tumbled Friday in the U.S. and abroad.

There have been no reported cases in the U.S. and there was no immediate indication whether the variant was more transmissible or causes more severe disease.

Dr. Paul Sax, the clinical director of the infectious disease clinic at Brigham and Women’s Hospital in Boston, said there’s not much known about it right now.

“So, a lot to be learned, a lot of uncertainty at this point, but I’m really glad and very excited that the scientists have reported this and that we can get to work on it quickly,” he told CNN Friday.

“Many of the cases that have been identified so far have actually been identified in people who are without symptoms and that is encouraging. It means that maybe the vaccines are still proving protection against severe disease, even if they have allowed people to have a breakthrough case.”

Dr. Sax said, so far, the coronavirus variants “have not conclusively shown that the disease becomes more severe.”

He believes we’ll hear a lot of information over the next week about experiments that are being done to track the new variant.

“I know that the people that I’ve communicated with, virologists, say that we should be able to tell relatively soon whether it’s circulating widely here. I suspect it isn’t because the only place it’s circulating widely, so far, has been in southern Africa, but at least we’ll be able to find out – is there a signal of early cases?”

Dr. Sax said travel bans have had a limited effect on the spread of the virus globally, so far.

He said the best way to be protected is to get a booster shot because it’s very likely the vaccines will prevent severe disease.

(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)