The vaccine developed by the University of Oxford and AstraZeneca not only protects people from serious illness and death but also substantially slows the transmission of the virus, according to a new study — a finding that underscores the importance of mass vaccination as a path out of the pandemic.

The study by researchers at the University of Oxford is the first to document evidence that any coronavirus vaccine can reduce transmission of the virus.

Researchers measured the impact on transmission by swabbing participants every week seeking to detect signs of the virus. If there is no virus present, even if someone is infected, it cannot be spread. And they found a 67 per cent reduction in positive swabs among those vaccinated.

The results, detailed by Oxford and AstraZeneca researchers in a manuscript that has not been peer-reviewed, found that the vaccine could cut transmission by nearly two-thirds.

Matt Hancock, the British health secretary, hailed the results on Wednesday as “absolutely superb”.

“We now know that the Oxford vaccine also reduces transmission and that will help us all get out of this pandemic,” Hancock said in an interview Wednesday morning with the BBC.