The Lowdown Hub

Double-jabbed people carry the same levels of Covid as unvaccinated Delta variant blamed for rising

As vaccinations are rolled out in venues such as nightclubs, the results of the study called into question the effectiveness of vaccine passports in such locations CREDIT: Henry Nicholls/Reuters

Fully vaccinated people carry the same amount of Covid as the unvaccinated, scientists have found in a new study that calls into question the effectiveness of vaccine passports and changes to the NHS app.

Experts had hoped two doses of vaccine would significantly reduce the viral load carried by people who became infected, lowering the risk of them passing on Covid.

Previous studies showed that vaccinated people who contracted the alpha variant had far lower viral loads than the unvaccinated, while Boris Johnson backed vaccine passports in the hope they would lower transmission in hotspot venues such as nightclubs. The NHS Covid app was also changed so double-jabbed people no longer need to self-isolate if pinged.

However, the new study by the University of Oxford shows that the delta variant wipes out the viral load reduction.

Instead, even the fully jabbed carry high levels of the virus if they become infected and are also more likely to be symptomatic than vaccinated people who pick up an alpha infection. The results suggest those who are fully jabbed could be as capable of passing on Covid as the unvaccinated, although they are less likely to pick up the virus in the first place.

Sarah Walker, professor of medical statistics and epidemiology at Oxford, and chief investigator and academic lead for the Covid-19 Infection Survey, said: "With alpha, people with two doses had really low levels of virus.

"When delta started to come in, the first thing that happened was that the virus values went up and now we really don't see any difference in the number of viruses people get if they get infected after vaccination.

"Two doses are still protective. You are still less likely to get infected, but if you do you will have similar levels of the virus as someone who hasn't been vaccinated at all."

The researchers said they were not sure whether high viral loads would translate into the same levels of transmission for vaccinated and unvaccinated people because the fully jabbed may clear the virus quicker and so be infectious for a shorter period of time. However, Prof Walker added: "The fact that they can have high levels of the 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, a 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 infection in the first place, which will have a role in stopping transmission. Two doses of the AstraZeneca jab lowered the rate of new infection by 67 percent and Pfizer by 82 percent. 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 hospitalization 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 hospitalized.

"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."

1 comment