The highly contagious Delta variant of coronavirus is the "greatest threat" to America's attempt to eradicate the Covid pandemic, the country's leading infectious disease expert Dr Anthony Fauci has warned.
The variant, which was first detected in India, is more contagious and causes more severe disease than other circulating variants, Dr Fauci, who is White House Chief Medical Advisor, has said.
Dr Fauci said the Delta variant now makes up more than 20% of all new cases in the US, doubling from nearly 10% two weeks ago.
He, however, added that the US vaccines are effective against the Delta variant.