A single dose of a Covid-19 vaccine can reduce transmission of the virus within a household by half, a study by Public Health England showed on Wednesday.

The study offers hope at a time when the pandemic is continuing to spread around the world, with more than 14.92 crore confirmed coronavirus cases and over 31.46 lakh deaths across nearly 200 countries since the virus first surfaced in China’s Wuhan in December 2019.

The research found that those who became infected three weeks after receiving a single dose of either the Pfizer-BioNTech or AstraZeneca-Oxford vaccines were between 38% and 49% less likely to pass the coronavirus on to people living in their homes, in comparison to those who were not inoculated.

A shot also stopped a person from developing symptomatic infection to begin with, reducing the risk of contracting the virus by 60% to 65% from four weeks after one dose of either of the vaccine. Protection was seen from about 14 days after vaccination, with similar levels regardless of a person’s age or contacts.

The study, however, is yet to be fully peer-reviewed.

The study by Public Health England included over 57,000 contacts from 24,000 households in which there was a lab-confirmed case of coronavirus after vaccination, compared with nearly 1 million contacts of unvaccinated cases.

Contacts were defined as secondary cases of coronavirus if they tested positive two to 14 days after the initial household case. Most of the people in the study were under the age of 60.

Read the full study here.

UK Health Secretary Matt Hancock described the results as “terrific news”. He added: “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.”

Hancock urged everyone to get vaccinated as soon as they were eligible.

Mary Ramsay, head of immunisation at Public Health England, said the findings were “very encouraging”. But she also urged individuals who had been vaccinated to continue to act responsibly, practise good hygiene and follow physical distancing guidelines to limit transmission.

Households are high-risk settings for transmission and the study provides early evidence on the impact of vaccines in preventing onward spread, the Public Health England said. Similar results could be expected in other settings with same transmission risks, like shared accommodation and prisons, it added.

“Vaccines are vital in helping us return to a normal way of life,” Ramsay said. “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.”