“South Africa has a quite high seroprevalence of prior infection, particularly after delta, and in some parts of South Africa up to 80 percent of people were exposed to previous infection,” she said. “We don’t think it’s a question of virulence, but more a question of exposure to vaccination and prior infection, so we would be cautious to try and interpret that this is a less virulent strain. We’ll have to see what happens in other parts of the world before we make a call on this.”