A study by the Cambridge University Hospitals National Health Service Foundation Trust and the University of Cambridge looked at healthcare workers in January, where similar numbers of both vaccinated and unvaccinated staff were screened.
It found that 26 out of 3,252, or 0.8%, tests from unvaccinated healthcare workers were positive. This compared with 13 out of 3,535, or 0.37%, tests from healthcare workers less than 12 days post-vaccination, and four out of 1,989, or 0.2%, tests from healthcare workers at 12 days or more post-vaccination.
“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,” said Dr. Mike Weekes, an infectious-diseases specialist, who led the study.
This suggests a fourfold decrease in the risk of asymptomatic COVID-19 infection among healthcare workers who have been vaccinated for more than 12 days, said the researchers, with the level of infection halved for those vaccinated less than 12 days. The study hasn’t been peer reviewed.
The Pfizer–BioNTech vaccine is administered in two doses. In the U.S., the interval between doses is three weeks, while in the U.K. the interval is up to 12 weeks.
A growing body of evidence shows how effective the Pfizer–BioNTech vaccine has been in the U.K. and Israel, two of the countries in the lead in mass vaccination.