GENEVA — Advisers to the World Health Organization are holding a special session Friday to flesh out information about a worrying new variant of the coronavirus that has been detected in South Africa, though a top expert says its impact on COVID-19 vaccines may not be known for weeks.

The technical advisory group on the evolution of COVID-19 was meeting virtually to discuss the so-called B.1.1.529 variant that has caused stock markets to swoon and led the European Union to recommend a pause in flights to southern Africa.

The group could decide if it’s a “variant of concern” — the most worrying type, like the well-known delta variant — or a “variant of interest,” and whether to use a Greek letter to classify it.

“We don’t know very much about this, yet. What we do know is that this variant has a large number of mutations, and the concern is that when you have so many mutations it can have an impact on how the virus behaves,” said Maria Van Kerkhove, WHO’s technical lead on COVID-19, in a social-media chat Thursday.

Fewer than 100 full genome sequences of the variant are so far available, she said.

“It will take a few weeks for us to understand what impact this variant has on any potential vaccines, for example,” Van Kerkhove said.

Reached by phone, advisory group chairman Dr. Anurag Agrawal, the director of Institute of Genomics and Integrative Biology in New Delhi, said it was too soon to comment on the variant. He said that more data was needed before he could add to the information that was already available.

“This is one to watch. I would say we have concern, but I think you would want us to have concern,” Van Kerkhove said. “We have people who are on this.”