Washington, Dec 21 (IANS): New Omicron subvariants BQ.1 and BQ.1.1 have accounted for about 70 per cent of new Covid-19 cases in the US as the country's overall caseload has surpassed 100 million, according to the latest estimates by the Centers for Disease Control and Prevention (CDC).

BQ.1.1 was estimated to make up about 38.4 per cent of circulating variants in the week ending December 17, and BQ.1 was estimated to make up 30.7 per cent, according to CDC data.

The two variants are descendants of Omicron's BA.5 subvariant and they have been growing especially fast since October, reports Xinhua news agency citing the data.

At the beginning of October, each of the two new variants accounted for about 1 per cent of new infections.

They replaced BA.5 to be dominant strains in mid-November.

BA.5 only accounted for 10 per cent of new infections in the latest week.

Another Omicron subvariant XBB is also on the rise, accounting for 7.2 per cent of new infections.

Researchers found that the BQ and XBB subvariants are "barely susceptible to neutralization" by the vaccines, including the new Omicron boosters, according to a study published recently in the journal Cell.

This could result in a surge of breakthrough infections and reinfections, though the vaccines have been shown to hold up against severe disease, according to the study.

In its latest update on Wednesday, according to data from the Johns Hopkins University.

As of Wednesday, the Johns Hopkins University said that country's overall caseload now stood at 100,003,814, while the death toll increased to 1,088,236.

With the highest number of cases and deaths, the US remains the worst-hit country in the world.

It accounts for more than 15 per cent of the global caseload and over 16 per cent of the overall fatalities.

The country's Covid caseload reached 50 million on December 13, 2021, crossed 60 million on January 9, 2022, exceeded 70 million on January 21, topped 80 million on March 29, and surpassed 90 million on July 21.