Just one dose of a Covid vaccine can cut transmission by up to half, a new study from Public Health England (PHE) has found.
According to the new study, people who received a single dose of either the Pfizer/BioNTech or Oxford/AstraZeneca vaccines – and who became infected at least three weeks later – were between 38 per cent and 49 per cent less likely to pass the virus on to people living in their homes, compared to unvaccinated people.
Regardless of a person’s age, similar levels of protection was seen from around 14 days after getting a jab.
The findings come after data published last week from the national Covid-19 Infection survey run by the University of Oxford and the Office for National Statistics (ONS) also found that vaccines are likely to cut transmission.
Just one dose of either the Pfizer or AstraZeneca vaccines cut coronavirus cases by two-thirds and were 74 per cent effective against symptomatic infection, according to the data.
Other studies have already shown that both vaccines are highly effective at stopping people from getting sick and having to be admitted to hospital for treatment.
Experts will now assess whether two doses of vaccine can cut transmission of Covid-19 even further, and more work is being carried out on transmission in the general population.
According to the ONS survey, there was a 70 per cent reduction in all cases and a 90 per cent drop in symptomatic cases after two doses of Pfizer. The latter are the people most likely to transmit coronavirus to others.
Similar results could be expected in places where the risk of transmission is similar to the home, said PHE, such as shared accommodation and prisons.
The study included data from January and February, when the variant of Covid-19 that first emerged in Kent was dominant in the UK.
Health secretary Matt Hancock called the findings “terrific news”, adding: “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.”
The study, which has yet to be peer-reviewed, included more than 57,000 people living in 24,000 households who were contacts of a vaccinated person.
They were compared with nearly a million contacts of people who had not had a vaccine. Contacts were defined as secondary cases of coronavirus if they tested positive two to 14 days after the initial household case.
Most of the study’s participants were under the age of 60.
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.”
Dr Peter English, a retired consultant in communicable disease control, said the study was robust and the authors may have in fact underestimated the effect of vaccines on transmission.
He added: “These findings are really important. They add to our reasons to hope that the vaccines will truly add to herd immunity.
“The evidence was already mounting that vaccination will prevent people from becoming infected, and if they aren’t infected, they can’t transmit the infection.
“This study shows that even if people who are vaccinated do become infected, they are considerably less likely to be infectious, and to pass the infection on to others. This is an extremely encouraging set of findings.”