Scientists have found that fully vaccinated people carry the same level of Covid-19 as the unvaccinated in a potential blow to the efficacy of the jabs.
Previous studies had shown that vaccinated people who caught the Alpha variant carried far lower viral loads than those who had not been vaccinated.
However, a study from the University of Oxford has found that the now-dominant Delta variant totally wipes out the viral load reduction.
Experts had hoped that being double-vaccinated would significantly reduce the viral load carried and thus lessen the chances of passing on the virus.
Instead, the fully vaccinated can carry high levels of the virus if they become infected and are more likely to experience symptoms than they were with the Alpha variant.
Although being less likely to catch Covid in the first place, the studies suggest that the fully vaccinated are now as capable of passing on the virus as the unvaccinated.
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 amount of virus 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 virus as someone who hasn’t been vaccinated at all.”
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.
Prof. Walker echoed those statistics in calling for those not already vaccinated to get their jabs.
“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.”