The government said the data supported Johnson’s decision to delay the end of Covid restrictions in England until July 19, citing the threat of the Delta variant first identified in India and the need to vaccinate more people.
The latest round of the REACT-1 prevalence survey, conducted between May 20 and June 7, found that the prevalence was 0.15%, compared with 0.10% in the last data set since late April to early May.
“The prevalence is increasing exponentially, driven by younger ages … and appears to be doubling every 11 days. Clearly, that’s bad news,” Steven Riley, professor of infectious disease dynamics at Imperial College London, told reporters.
The study is one of Britain’s largest prevalence surveys, with 109,000 volunteers screened in its latest round.
Riley added that Britain’s high vaccination levels make it difficult to predict how long that exponential growth will last, and said the rapid deployment of vaccine doses to younger age groups should slow it down.
More than half of Britain’s adult population has received two doses of vaccine and more than three-quarters of adults have received at least one dose of vaccine.
Although the Delta variant has been 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.
“These findings highlight the harsh context in which we made the difficult decision to delay step 4 of the roadmap out of the lockdown,” said Health Minister Matt Hancock, referring to the lifting of the last remaining restrictions in England.
“We all need to stay on our nerves a little longer as our vaccine launch continues.”