Los Angeles, Dec 31 : New Omicron subvariant XBB.1.5 is estimated to account for 40.5 per cent of Covid-19 cases in the US in the week ending December 31, nearly doubling from the previous week, according to data updated by the US Centers for Disease Control and Prevention (CDC). XBB.1.5 made up 21.7 per cent of the total cases in the previous week ending December 24, Xinhua news agency reported. Recombinants of the BA.2 variant, XBB and XBB.1.5 together accounted for 44.1 per cent of the total cases in the country in the week ending December 31, CDC data showed. The XBB variant has been driving up cases in parts of Asia, drawing concerns for its high infectiousness. Another two Omicron subvariants BQ.1 and BQ.1.1 accounted for about 45 per cent of new Covid-19 cases in the US in the latest week, CDC data showed. /IANS