The Delta variant of the coronavirus is the cause of more than 80 percent of new US Covid-19 cases, but the authorised vaccines remain more than 90 percent effective in preventing hospitalisations and deaths, said top US infectious disease expert Anthony Fauci during a US Senate hearing on Tuesday.

The hearing featured a pointed exchange with Republican US Senator Rand Paul, in which he accused Fauci of lying about the National Institutes of Health providing funding for research at China's Wuhan Institute of Virology...