Late in November, the World Health Organization designated the Covid variant B.1.1.529, with its many mutations, as a variant of concern. Dubbed Omicron, within weeks it had rapidly spread across the globe and become the dominant variant. But not far behind has been its even more transmissible cousin, BA.2. Initially taking off in Denmark and India, BA.2 is now making headway in several countries around the world, including the US and UK. Ian Sample speaks to Prof Nick Loman about how worried we should be about BA.2, and what we still need to learn about this new subvariant. Help support our independent journalism at theguardian.com/sciencepod