A single dose of Pfizer and BioNtech’s Covid-19 vaccine could significantly reduce the risk of transmission of the virus, a UK study has found.
Researchers analysed results from thousands of Covid-19 tests carried out each week as part of hospital screenings of healthcare staff in Cambridge.
Mike Weekes, an infectious disease specialist at Cambridge University’s department of medicine, who co-led the study, said: “This is great news – the Pfizer vaccine not only provides protection against becoming ill from SARS-CoV-2, but also helps prevent infection, reducing the potential for the virus to be passed on to others.
“But we have to remember that the vaccine doesn’t give complete protection for everyone.”
The study also found a single dose of the jab cuts the number of asymptomatic infections.
“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, an infectious diseases specialist at Cambridge University Hospital, another co-lead on the study.
After separating the test results from unvaccinated and vaccinated staff, Jones’ team found that 0.80% tests from unvaccinated healthcare workers were positive.
This compared with 0.37% of tests from staff less than 12 days post-vaccination – when the vaccine’s protective effect is not yet fully established – and 0.20% of tests from staff at 12 days or more post-vaccination.
The study and its results have yet to be independently peer-reviewed by other scientists, but were published online on Friday.
This suggests a four-fold decrease in the risk of asymptomatic Covid-19 infection amongst healthcare workers who have been vaccinated for more than 12 days, and 75% protection, said Weekes.
The level of asymptomatic infection was also halved in those vaccinated for less than 12 days, he said.
Britain has been rolling out vaccinations with both the Pfizer Covid-19 shot and one from AstraZeneca since late December 2020.
Key real-world data published on Wednesday from Israel, which has conducted one of the world’s fastest rollouts of Pfizer’s Covid-19 vaccine, showed that two doses of the Pfizer shot cut symptomatic Covid-19 cases by 94% across all age groups, and severe illnesses by nearly as much.
Prof Lawrence Young, professor of molecular oncology at Warwick Medical School, said: “These studies are very encouraging because they suggest that the vaccines will prevent the spread of the virus. You can’t spread the virus if you’re not infected and these studies show that the vaccine blocks infection in individuals who don’t have symptoms but could pass on the infection.”
