The first NHS data has shown that a single dose of the Pfizer vaccine dramatically reduces symptomless Covid-19 cases from passing on the virus.
The findings from Addenbrooke’s Hospital in Cambridge indicated 75% protection and suggest that as well as reducing deaths the vaccination programme will bring infections down quickly.
Cambridge University researchers found that one dose reduced by four-fold the number of asymptomatic coronavirus infections once immunity developed 12 days later.
Vaccination for health care workers began on December 8 with mass vaccination from January 8.
Researchers screened similar numbers of vaccinated and unvaccinated staff between January 18 and 31 using around 4,400 PCR tests per week.
The findings also appear to endorse the safety of the UK’s decision to delay second doses for up to 12 weeks.
Pfizer had only trialled the effectiveness of its vaccine after two doses, three weeks apart.
Study lead Dr Mike Weekes 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.
“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.”
The study found that 26 out of 3,252 (0·80%) tests from unvaccinated healthcare workers were positive.
This compared to 13 out of 3,535 (0.37%) tests from healthcare workers less than 12 days after vaccination.
This dropped to just four positive tests out of 1,989 (0·20%) at 12 days or more post-vaccination.
Co-author Dr Nick Jones said: “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.
“This is fantastic news for both hospital staff and patients, who can be reassured that the current mass vaccination strategy is protecting against asymptomatic carriage of the virus in addition to symptomatic disease, thereby making hospitals even safer places to be.”
