LONDON (Reuters) – A single dose of Pfizer and BioNtech’s COVID-19 vaccine reduces the number of asymptomatic infections and could significantly reduce the risk of virus transmission, according to a UK study found on Friday.
The researchers analyzed the results of thousands of COVID-19 tests performed each week as part of hospital tests of healthcare staff in Cambridge, in the east of England.
“Our findings show a dramatic reduction in the rate of positive screening tests among asymptomatic health workers after a single dose of the Pfizer-BioNTech vaccine,” said Nick Jones, an infectious disease specialist at University Hospital of Cambridge, who led the study.
After separating the test results from unvaccinated staff and vaccinated staff, the Jones team found that 0.80% of tests for unvaccinated health workers were positive.
This compares with 0.37% of tests performed by staff less than 12 days after vaccination (when the protective effect of the vaccine is not yet fully established) and 0.20% of tests performed by staff 12 days or more after vaccination.
The study and its results have not yet been independently reviewed by other scientists, but were published online as a prepress on Friday.
This suggests a four-fold decrease in the risk of asymptomatic COVID-19 infection among health workers vaccinated for more than 12 days and 75% protection, said Mike Weekes, an infectious disease specialist in the University of Medicine’s medical department. Cambridge, who co-directed the study.
The level of asymptomatic infection was also halved in those vaccinated for less than 12 days, he said.
Britain has deployed vaccines with both the Pfizer COVID-19 and one AstraZeneca shot since late December 2020.
“This is great news: the Pfizer vaccine not only provides protection against SARS-CoV-2 disease, but also helps prevent infection, reducing the potential for transmission of the virus to others,” Weeks said. “But we must remember that the vaccine does not provide complete protection for everyone.”
Key real-world data released Wednesday from Israel, which carried out one of the world’s fastest launches of Pfizer’s COVID-19 vaccine, showed that two doses of Pfizer’s shot reduced symptomatic cases of COVID -19 in 94% in all age groups and serious illnesses almost as much.
Reports by Kate Kelland; Edited by David Goodman and Jane Merriman