WASHINGTON (REUTERS) - The fast-spreading BA.4 and BA.5 sub-lineages of Omicron are estimated to make up a combined 70.1 per cent of the coronavirus variants in the United States as of July 2, the US Centres for Disease Control and Prevention said on Tuesday (July 5).

BA.4 and BA.5 made up 52 per cent of US variants for the week of June 25. They were added to the World Health Organisation's monitoring list in March and designated as variants of concern by the European Centre for Disease Prevention and Control.

The US Food and Drug Administration recommended last week that Covid-19 vaccine makers change the design of their booster shots beginning this autumn to include components tailored to combat BA.4 and BA.5.

BA.4 made up 16.5 per cent of the variants in circulation, the latest data showed, while BA.5 accounted for 53.6 per cent.