The prevalence of XBB.1.5 has kept increasing since late last year, and it is estimated to account for 89.2 per cent of new Covid-19 cases in the country this week, up from 85.4 per cent last week and 79.7 per cent two weeks prior, reports Xinhua news agency.
The second most prevalent strain BQ.1.1 accounts for 6.7 per cent. The CDC first started tracking XBB.1.5 in November last year, when it accounted for less than 1 per cent of cases nationwide.
Since then, the strain is spreading quickly in the US. Early study suggests XBB.1.5 has a couple of concerning mutations that suggest it is even more contagious than other strains, possibly the most transmissible one so far.
While XBB.1.5 is spreading easier, scientists said it does not seem to cause more severe disease.