The findings from Addenbrooke’s Hospital in Cambridge indicated 75-per-cent protection from Covid-19.

The results also point to a four-fold decrease in the risk of asymptomatic Covid infection among healthcare workers who have been vaccinated for more than 12 days – suggesting the first dose will significantly reduce the spread of the virus.

“Our findings show a dramatic reduction in the rate of positive screening tests among asymptomatic healthcare workers after a single dose of the Pfizer-BioNTech vaccine,” said Nick Jones, a Cambridge University Hospital specialist who co-led the study.