The BA.5 Omicron sub-variant, now the dominant coronavirus strain in the US, accounts for over 80 per cent of the new cases in the country, according to the latest data from the Centers for Disease Control and Prevention (CDC).
The sub-variant accounted for 81.9 per cent of the new infections in the week ending July 23, Xinhua news agency quoted the CDC as saying.
Another new sub-variant, BA.4, accounted for 12.9 per cent of new infections, CDC data showed.
The two contagious sub-variants now make up over 90 per cent of new infections in the US.
Confirmed cases contracted by the two sub-variants have kept increasing since mid-May, CDC data showed.
BA.5 has been driving a surge of new infections in the US and globally.
It appears to be more contagious and better at evading protection from vaccines and previous infections than most of its predecessors, study showed.
US health officials are urging people aged 50 or older to get a booster shot to better protect against severe diseases from Covid-19.