The Delta variant of Covid-19 is the cause of more than 80 per cent of the new cases in the United States, but the authorised coronavirus vaccines in the country are still more than 90pc effective in preventing hospitalisations and deaths, said top US infectious disease expert Anthony Fauci during a Tuesday US Senate hearing, according to Reuters.

The highly contagious Delta variant was first found in India earlier this year. It has since become the dominant strain of Covid-19 in the United States and has been detected in more than 90 countries worldwide.

Deaths from Covid-19 in the United States have averaged 239 per day over the past week, nearly 48pc higher than the previous week, US Centers for Disease Control and Prevention Director Rochelle Walensky said during the hearing.