Two doses of the Pfizer one also dramatically cuts the chance of passing the virus on.
Public Health Scotland and the University of Glasgow assessed 300,000 NHS workers and their households between December 8 – the first day of vaccination in Scotland – and March 3 to give the first direct knowledge of how the jabs impact transmission.
The study assessed the records of people who live with both vaccinated and unvaccinated healthcare workers, and found the rate of Covid-19 among them was at least 30% lower when the health worker had had a single dose.
Given that people living with healthcare workers could also catch the virus from other sources, researchers said the 30% figure is a low estimate.
For those living with workers who had both doses of either vaccine, their risk of Covid was found to be at least 54% lower.
Dr Dianne Stockton, the Public Health Scotland lead for the Covid-19 Vaccination Surveillance Programme, said the results are “encouraging”, but stressed this should not make the public complacent.
“Despite this good news, it is important to remember that infection prevention and control practices in healthcare settings remain of paramount importance, as do the mitigations to prevent spread in our daily lives,” she said.
The risk of transmission did not go down to zero after individual healthcare workers were vaccinated.
Dr Stockton added: “As Scotland continues to deliver its national Covid-19 vaccination programme, this study does give one more reason why everyone invited to have a vaccine should take up the offer, as not only will it help protect them from Covid-19, but it will help protect the people close to them.”
Dr David McAllister, of Glasgow University, said: “Our study has important implications for informing vaccination strategies.
“The Joint Committee on Vaccination and Immunisation in the United Kingdom recently commented on the lack of real-world evidence evaluating the role of vaccination programmes on transmission.
“We provide the first direct evidence that vaccinating individuals working in high-exposure settings reduces the risk to their close contacts – members of their households.
“Our work will also be of interest to modellers, as it can be used to inform their predictions about future rates of Covid-19 in the community.”
Speaking at the Scottish Government’s coronavirus briefing on Friday, Health Secretary Jeane Freeman said: “It’s obviously very encouraging data indeed.
“We’ve already seen the impact the vaccination programme is having on deaths in care homes and increasingly in the community.
“Today’s study adds to the growing evidence that vaccination can also help reduce the transmission of the virus.”