Los Angeles, Jan 21 : New Omicron subvariant XBB.1.5 is estimated to account for 49.1 per cent of the Covid-19 cases in the US for the week ending January 21, according to data released by the US Centers for Disease Control and Prevention (CDC). The subvariant XBB.1.5 is spreading quickly in the US. It made up 35.5 per cent of the total cases in the week ending January 7, rising to 37.2 per cent in the week ending January 14, according to the CDC on Friday. XBB.1.5 is currently the most transmissible variant in the country. The subvariant may spur more Covid-19 cases based on genetic characteristics and early growth rate estimates, according to the WHO as quoted by Xinhua news agency report. Another two dominant Omicron subvariants BQ.1 and BQ.1.1 accounted for about 40 per cent of new Covid-19 cases in the US in the latest week, CDC data showed. /IANS