Studies have already demonstrated that being vaccinated against coronavirus (COVID-19) significantly reduces your risk of being infected.
This new research shows that those who do become infected 3 weeks after receiving one dose of the Pfizer-BioNTech or AstraZeneca vaccine were between 38% and 49% less likely to pass the virus on to their household contacts than those who were unvaccinated.
Protection was seen from around 14 days after vaccination, with similar levels of protection regardless of age of cases or contacts.
This protection is on top of the reduced risk of a vaccinated person developing symptomatic infection in the first place, which is around 60 to 65% – 4 weeks after one dose of either vaccine.
Households are high-risk settings for transmission and provide early evidence on the impact of vaccines in preventing onward transmission. Similar results could be expected in other settings with similar transmission risks, such as shared accommodations and prisons.
By linking case and household contact data with vaccination status, the study compared the likelihood of transmission for a vaccinated case with an unvaccinated one.
The study included over 57,000 contacts from 24,000 households in which there was a lab-confirmed case that had received a vaccination, compared with nearly 1 million contacts of unvaccinated cases.
Health and Social Care Secretary, Matt Hancock, said:
This is terrific news – we already know vaccines save lives and this study is the most comprehensive real-world data showing they also cut transmission of this deadly virus.
It further reinforces that vaccines are the best way out of this pandemic as they protect you and they may prevent you from unknowingly infecting someone in your household.
I urge everybody to get their vaccines as soon as they are eligible and make sure you get your second dose for the strongest possible protection.
This is a huge national effort and we will beat the virus together.
Dr Mary Ramsay, Head of Immunisation at PHE, said:
Vaccines are vital in helping us return to a normal way of life. Not only do vaccines reduce the severity of illness and prevent hundreds of deaths every day, we now see they also have an additional impact on reducing the chance of passing COVID-19 on to others. I encourage anyone who is offered a vaccine to take it as soon as possible.
While these findings are very encouraging, even if you have been vaccinated, it is really important that you continue to act like you have the virus, practise good hand hygiene and follow social distancing guidance.
Previous PHE studies have shown that both the Pfizer-BioNTech and AstraZeneca vaccines are highly effective in reducing COVID-19 infections among older people, with 10,400 deaths prevented in the over-60s by the end of March.
PHE is also undertaking separate studies on the effect of vaccination on transmission in the wider population.