Researchers in South Africa are racing to track the concerning rise of a new variant of the coronavirus that causes COVID-19. The variant harbours a large number of mutations found in other variants, including Delta, and it seems to be spreading quickly across South Africa. A top priority is to track the variant more closely as it spreads: it was first identified in Botswana this month and has turned up in travellers to Hong Kong from South Africa. Scientists are also trying to understand the variant’s properties, such as whether it can evade immune responses triggered by vaccines and whether...