This winter has seen the emergence of a new sub-variant of SARS-CoV-2, the virus that causes COVID-19. This sub-variant – XBB1.5, or ‘Kraken’ – is the daughter of the globally-dominant Omicron. Professor Ravi Gupta from the Cambridge Institute of Therapeutic Immunology and Infectious Disease tells us everything we need know about the sub-variant – and why it has surprised the scientific community.