‌The World Health Organisation (WHO) reports that the XFG variant is the newest COVID-19 strain and is currently the most widespread in the UK. Besides Stratus, another strain being monitored is NB.1.8.1, known as Nimbus. ‌Similar to Stratus, it's believed to be highly contagious, but it doesn't appear to be any more serious than other Omicron variants. Coronavirus: WHO explains how COVID-19 is transmitted‌Since September, the WHO reports that the main COVID-19 strain in the UK is the Stratus variant, which is the Omicron subvariant XFG and its offshoots, particularly XFG.3. The NHS says: "The symptoms are very similar to symptoms of other illnesses, such as colds and flu.