The rapid spread of the Delta coronavirus variant first identified in India has driven a 50 percent rise in infections in England since May, a large study led by Imperial College London found on Thursday.

Iran PressEurope: The British government said the data supported Boris Johnson's decision to delay the end of Covid-19 restrictions in England to July 19, given the threat of the Delta variant and the need to vaccinate more people.

According to British media, the latest round of the React-1 survey, conducted between May 20 and June 7, found prevalence was 0.15 percent, compared to 0.10 percent in the last set of data from late April to early May.

"Prevalence is increasing exponentially, driven by younger ages ... and it appears to be doubling every 11 days. Clearly, that is bad news," said Steven Riley, professor of infectious disease dynamics at Imperial College London.

The study is one of the largest prevalence surveys in Britain, with 109,000 volunteers tested in its latest round.

More than half of the adult population of Britain have received two vaccine doses, and more than three-quarters of adults have received at least one.

Although the Delta variant is shown to substantially reduce the effectiveness of one dose of vaccine against mild infection, two doses still provide good protection against severe disease, early evidence has shown. 219