Story at a glance

  • Researchers from Cambridge University Hospitals NHS Foundation Trust (CUH) and the University of Cambridge analyzed results from thousands of COVID-19 tests conducted among staff.
  • Over a two-week period in January, researchers tested similar numbers of vaccinated and unvaccinated staff for COVID-19 using PCR lab tests.
  • They found that 0.8 percent of tests from unvaccinated health care workers were positive, compared with 0.37 percent of tests from vaccinated staff less than 12 days post-vaccination. Among staff tested more than 12 days after receiving the dose, just 0.2 percent of tests were positive.

A new study out of the U.K. found a single dose of the Pfizer-BioNTech COVID-19 vaccine can significantly reduce asymptomatic infections, suggesting the shot could cut the risk of transmission as well as protect people from becoming ill from the virus. 

Researchers from Cambridge University Hospitals NHS Foundation Trust (CUH) and the University of Cambridge analyzed results from thousands of COVID-19 tests conducted weekly as part of screening of hospital staff who showed no signs of infection. 


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Over a two-week period in January, researchers tested similar numbers of vaccinated and unvaccinated staff for COVID-19 using PCR lab tests. They then compared infection rates among unvaccinated staff and those who received the first dose of the vaccine more than 12 days prior to testing — the amount of time it takes for the body to produce an immune response. 

The study, which has yet to be peer-reviewed, found that 0.8 percent of tests from unvaccinated health care workers were positive, compared with 0.37 percent of tests from vaccinated staff less than 12 days post-vaccination. Among staff tested more than 12 days after receiving the dose, just 0.2 percent of tests were positive. 

The results suggest a fourfold decrease in the risk of asymptomatic COVID-19 infection among health care staff who have been vaccinated for more than 12 days and 75 percent protection. 

“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,” Mike Weekes, an infectious disease specialist at CUH and the University of Cambridge’s Department of Medicine who led the study, said in a statement

“This will be welcome news as we begin to plot a roadmap out of the lockdown, but we have to remember that the vaccine doesn’t give complete protection for everyone. We still need social distancing, masks, hand hygiene and regular testing until the pandemic is under much better control,” Weekes said. 

The Pfizer-BioNTech vaccine requires two doses administered several weeks apart. 

The research comes as a pair of British studies published in The Lancet Thursday found that a single dose of the vaccine may offer significant protection for those who have already been infected with COVID-19. 


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Published on Feb 26, 2021