Study Shows 1 Dose of Covid-19 Vaccine

A single dose of a coronavirus vaccine can reduce household transmission of the virus by up to half, a study shows.

Those given the first dose of either the Pfizer or AstraZeneca vaccines – and who became infected three weeks later – were between 38% and 49% less likely to pass the virus on than unvaccinated people, PHE found.

Health Secretary Matt Hancock described the study’s results as “terrific news”.

He has urged “everybody to urge their vaccines as soon as they’re eligible”.

In the study, protection against Covid was seen from about 14 days after vaccination, with similar levels of protection no matter age of cases or contacts, PHE said during a statement.

It added that this protection was on top of the reduced risk of a vaccinated person developing symptomatic infection within the first place, which is around 60 to 65% – four weeks after one dose of either vaccine.

Dr. Mary Ramsay, head of immunization 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 stop many deaths a day, we now see they even have a further impact on reducing the prospect of passing Covid-19 on to others.”

But, while she said the findings were “encouraging”, she said it was important people continue to act like they have the virus, “practice good hand hygiene and follow social distancing guidance”.

Households are high-risk settings for transmission, meaning the study provides early evidence on the impact of vaccines in preventing onward transmission, PHE said.

Similar results could be expected in other settings with similar transmission risks, such as shared accommodation and prisons, it added.

The study, which has yet to be fully peer-reviewed, included quite 57,000 contacts from 24,000 households during which there was a lab-confirmed coronavirus case that had received a vaccination, compared with nearly a 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 within the study were under the age of 60.

Previous PHE studies have shown that both the Pfizer-BioNTech and Oxford-AstraZeneca vaccines are highly effective in reducing Covid-19 infections among older people, with 10,400 deaths prevented in over-60s by the end of March.

PHE is additionally undertaking separate studies on the effect of vaccination on transmission within the wider population.

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