New data from Addenbrooke's hospital in Cambridge suggests a significant drop in the spread of Covid-19 amongst staff following vaccination.
It's one of the first indications from UK scientists that the Pfizer vaccine reduces the transmission of SARS-CoV-2, the virus that causes Covid-19, as well as protecting people from getting ill.
The study by Cambridge University Hospitals NHS Foundation Trust (CUH) and the University of Cambridge analysed data from thousands of Covid-19 tests carried out each week on hospital staff who showed no signs of infection.
The findings show a dramatic drop in the rate of positive tests amongst asymptomatic staff following vaccination.
Dr Michael Weekes led the study and is an honorary consultant in infectious diseases at CUH.
Two weeks after a single dose of the Pfizer Covid-19 vaccine, hospital staff became four time less likely to become infected with CoronavirusDr Michael Weekes
Dr Michael Weekes
Transcript of video clip
"What we found was that about two weeks after a single dose of the Pfizer Covid-19 vaccine, hospital staff became four times less likely to become infected with Coronavirus.
"And our study is important because we specifically examined staff who had no symptoms of infection, and so they didn't know they were infected with Coronavirus and therefore were particularly likely to transmit the infection on to others.
"And so what this means is four times less transmissions to colleagues. Four times less transmissions to vulnerable patients. And this means that hospitals will be even safer places to be cared for and to work.
"However, the vaccine does not completely prevent transmission. And so social distancing, mask wearing, regular testing and hand washing remain as important as ever."
Vaccination for health care workers on the CUH site began on 8 December 2020, with mass vaccination of staff from 8 January 2021.
During two weeks between 18 to 31 January this year, the study team screened similar numbers of vaccinated and unvaccinated staff using around 4,400 PCR tests per week.
The results were then separated out into staff who were unvaccinated, and staff who had been vaccinated for more than 12 days (when it's thought protection against infection occurs).
Analysis of the data suggests a four-fold decrease in the risk of asymptomatic Covid-19 infection amongst health care workers who have been vaccinated for more than 12 days (75 per cent protection). The level of asymptomatic infection was also reduced in those vaccinated for less than 12 days.
Dr Nick Jones, who is first author on the study and an infectious diseases/microbiology registrar at CUH, said: “Our findings show that the current mass vaccination strategy is protecting against asymptomatic carriage of the virus in addition to symptomatic disease".
This is fantastic news for both staff and patients, making hospitals even safer places to beDr Nick Jones
The study is yet to be peer-reviewed but has been published here (opens in a new tab).
This work was supported by Wellcome, the Medical Research Council, NHS Blood & Transplant, Addenbrooke’s Charitable Trust and the NIHR Cambridge Biomedical Research Centre.
Thanks to all the staff from CUH who have been involved in setting up, delivering and taking part in the testing and vaccination programmes.