The highly transmissible Omicron subvariant XBB.1.5 now accounts for 85 per cent of all Covid-19 cases reported in the US this week, according to the latest estimates of CDC The highly transmissible Omicron subvariant XBB.1.5 now accounts for 85 per cent of all Covid-19 cases reported in the US this week, according to the latest estimates of CDC News