XBB strain of Covid-19 is sparking health concerns as the new Omicron variant leads a surge in cases across the globe.Japanese researchers discovered in January 2023 that the subvariant is deemed highly transmissible and has developed resistance to immunity.XBB is a subvariant of the Omicron BA.2 variant, and XBB.1.5 is a subvariant of XBB.There is no evidence that XBB “is more deadly or causes more severe Covid-19 than the Delta variant”, according to a fact-checking article conducted by Reuters in November 2022.The XBB variant has now reportedly accounted for 40 per cent of cases in the US.Effective from 5 January 2023, the UK and US governments require all passengers travelling from China to return a negative Covid result before travelling.