New data from the ongoing trials and rollout of the Oxford/AstraZeneca Covid vaccine shows that it could reduce transmission of the virus.
When vaccine candidates first started reporting their trial results, data showed that several candidates reduced the risk of disease by up to 90%. They showed more than enough evidence of high effectiveness and low side-effect rates to be rapidly approved around the world for general use.
The effectiveness of the vaccines on reducing disease is impressive, but it's not the whole story as there are other variables that needed to be studied. We didn't have the data to show whether the vaccine prevented people from transmitting the virus in addition to reducing their own chance of disease, for example, or on how much protection a single shot gives before the second booster shot.
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Data on how the vaccine affects transmission is extremely important because it makes the difference between a vaccine just protecting the people who take it versus also protecting those around them. We know that many people pass on the virus that causes Covid-19 asymptomatically before their immune system responds, so it's possible that a vaccine could not affect transmission.
New studies on the Oxford/Astrazeneca vaccine has shown that it does seem to be effective at preventing transmission of the virus to others. The study monitored those who took the vaccine and took regular swabs to test for the presence of the virus, which would indicate it's being exhaled and could be transmitted.
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Early data from the study, which has yet to be formally published, demonstrated 76% effectiveness after three months of being given the first dose, with negative testing confirming no presence of the virus. This means that most of those who get a single shot of the vaccine should be protected personally and also unable to transmit the virus to others.
These results are promising support for the UK's vaccination strategy, which is emphasising giving as many people as possible their first dose quickly by delaying the second booster shot. It also shows that once enough people are vaccinated, we should develop nation-wide herd immunity that can protect those who are unable to take the vaccine due to medical complications. In the long run, it means we could get back to business as usual by next year.
