The original SARS-CoV-2 Omicron variant, now known as BA.1, hit the UK hard over winter 2021-22, causing a big wave of infections and putting huge pressure on hospitals.
But in late January 2022 it was noted that a second variation of Omicron, BA.2, was starting to spread around the world.
BA.2 is significantly more transmissible than BA.1, although it is still not clear whether it causes more severe disease.
Speaking to The BMJ, Eric Topol, professor of molecular medicine at the Scripps Research Institute in California, said: “I would attribute this to the ‘BA.2 triad.’ The variant has 30 percent more transmissibility than BA.1, but spread has been further enhanced by relaxed mitigation measures and waning of vaccine immunity. It’s all intertwined and clearly going to lead to more widespread surges, including in the US.”