Here’s the impact of a single vaccine dose on COVID-19 transmission

Here’s the impact of a single vaccine dose on COVID-19 transmission

A single dose of either the Oxford/AstraZeneca or Pfizer/BioNTech vaccines have been found to cut Covid-19 transmission rates by up to half, according to a new Public Health England (PHE) study this week.

Those given a first dose of either of the two vaccines currently being administered by the National Health Service (NHS) and who became infected with SARS-Cov-2 – the coronavirus which causes Covid-19 – three weeks later were between 38 and 49 per cent less likely to pass the virus on than unvaccinated people. The PHE also found that protection against Covid-19 was seen from about 14 days after vaccination, with similar levels of protection regardless of age of cases or contacts.

“A new study shows one dose of the vaccine can cut the risk of household transmission by up to 50 per cent. This is further evidence that the vaccine protects you and those around you. When you get the call, get the jab,” said UK Health Secretary Matt Hancock.

The study, which is yet to be fully peer-reviewed, included more than 57,000 contacts from 24,000 households in which there was a lab-confirmed coronavirus case that had received a 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.


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The protection against transmission was found on top of the reduced risk of a vaccinated person developing symptomatic infection in the first place, which has previously been found to be around 60 to 65 per cent – four weeks after one dose of either vaccine.

"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," said Dr Mary Ramsay, head of immunisation at PHE.

While the findings are seen as "encouraging", the PHE is calling on people continue with safety measures against transmission such as "practise good hand hygiene and follow social distancing guidance".

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