Full vaccination halves the transmission of the Delta variant of coronavirus and is 60 per cent effective at preventing symptoms of Covid-19, according to Imperial College’s latest React-1 prevalence survey.

The findings, released on Wednesday and based on a study of 98,000 volunteers in England, provide the most extensive community evidence so far of the way vaccines protect against Delta, which originated in India and has completely displaced the earlier Alpha variant in the UK since the beginning of April.

Recent studies have shown 90 per cent vaccine effectiveness in preventing hospitalisation with Delta. In React-1, 40 per cent of participants testing positive were asymptomatic and many others had very mild symptoms. Effectiveness estimates always decrease as researchers include less serious disease.