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 emerged 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.