I'm embarrassed for him.
:strip_exif(true):strip_icc(true):no_upscale(true):quality(65)/cloudfront-us-east-1.images.arcpublishing.com/gmg/JG3JTQ7TUBBAPORT3V45WAIQ3U.jpg)
However, Prof Walker added: "The fact that they can have high levels of virus suggests that people who aren't yet vaccinated may not be as protected from the delta variant as we hoped.
"It comes back to this concept of herd immunity, and the hope that the unvaccinated could be protected if we could vaccinate enough people. But I suspect the higher levels of the virus in vaccinated people are consistent with the fact that unvaccinated people are still going to be at high risk."
People who are double jabbed no longer need to be quarantined if they are pinged by the Covid app, but the new results suggest there could still be a risk even among the fully vaccinated.
Dr Koen Pouwels, senior researcher at Oxford University's Nuffield Department of Population Health, said: "Whilst vaccinations reduce the chance of getting Covid-19, they do not eliminate it.
"More importantly, our data shows the potential for vaccinated individuals to still pass Covid-19 onto others and the importance of testing and self-isolation to reduce transmission risk."
Despite the findings, the study showed the jabs are still helpful in preventing an infection in the first place, which will have a role in stopping transmission. Two doses of the AstraZeneca jab lowered the rate of a new infection by 67 per cent and Pfizer by 82 per cent.
The research, not yet peer-reviewed, also showed that while two doses of the Pfizer jab are initially more effective, four to five months after the second dose it is the same as the AstraZeneca vaccine.
The team studied 384,543 people who picked up an infection between December and May, when the alpha variant was dominant, before comparing them to 358,983 people infected between May and August, when delta had taken over.
Prof Walker said that even if the jabs did not stop transmission, they were likely to prevent hospitalisation and death.
"There are lots of reasons why the vaccines may be very good at reducing the consequences of having the virus," she added. "You may well still have a milder infection and might not end up getting hospitalised.
"While the results are important, they aren't everything and it is really important to remember the vaccines are super-effective at preventing hospitalisations."
Prof Paul Hunter, professor in medicine at the University of East Anglia, said: "We now know that vaccination will not stop infection and transmission, although they do reduce the risk.
"The main value of immunisation is in reducing the risk of severe disease and death. The evidence available shows that protection lasts longer against severe disease than against mild disease, and all current UK vaccines are very good at this, even against the delta variant. To me, that is the most important value of immunisations."
