Washington, Nov 1 (IANS): Covid-19 cases caused by new variants are growing fast in the US, according to data released by the Centers for Disease Control and Prevention (CDC).

According to the latest CDC data published on Monday, two new variants, BQ.1 and BQ.1.1, have been growing especially fast, reports Xinhua news agency.

At the beginning of October, each one accounted for about 1 per cent of new infections in the US, but they have been roughly doubling in prevalence each week, the health body said.

The data further revealed that BQ.1 led to about 14 per cent of new infections in the country in the week ending October 29, while BQ.1.1 caused 13.1 per cent of the fresh cases.

Together, the two variants accounted for more than one in four new infections nationwide, CDC data showed.

BA.5, which has dominated Covid-19 infections in the US since July, now accounted for 49.6 per cent of new cases in the country.

A host of new sublineages -- offshoots of BA.2, BA.4 and BA.5 -- are now responsible for the majority of new cases.

These variants are slightly different from each other, but they all carry some of the same key mutations that help them skirt immunity from vaccines and past infections. This makes them more likely to lead to breakthrough infections and reinfections, according to experts.

"BQ is actually a BA.5 variant," Dr. Andrew Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, recently told Health.

"Here in the US, all the variants that are circling -- BQ.1.1, I guess, is the biggest or the most talked about one now -- they're all derived from either the BA.5 or the BA.4 variants. They've picked up a few mutations that help them evade some of the infection or vaccine-induced immunity."

Another variant, XBB, is also a variant of Omicron and has been dubbed the "nightmare variant" in Singapore. It is extremely immune evasive and has also shown that it might be immune to current vaccines.

The World Health Organization (WHO) SARS-CoV-2 virus evolution advisory group said last week that XBB and BQ.1 do not currently diverge sufficiently from each other or from other Omicron lineages that have extra immune escape mutations to warrant a variant of concern designation or a new label.

"The two sublineages remain part of Omicron, which continues to be a variant of concern," the WHO group said.

Health experts are concerned emerging Omicron subvariants would make some existing protections ineffective for the public, especially the immunocompromised people.

"We're in a very challenging phase," said Syra Madad, an epidemiologist who helps oversee pandemic response for New York City Health and Hospitals, the nation's largest municipal health-care system.

"Barely anybody is masking. We have very low vaccination rates for the updated boosters, as well as generally waning immunity. And to top it all off, we have these highly immune-evasive subvariants that are circulating," Madad told The Washington Post on Monday.

The Covid-19 vaccination rate in the US lags that of many other high-income countries.

Less that half of the total booster-eligible population in the US has received a booster dose, according to CDC data.

Experts are urging the public to get booster shots to prevent from severe illnesses.

As of Tuesday, the country's overall Covid caseload and death toll stood at 99,374,721 and 1,095,315, respectively.

The two tallies are the highest in the world.