Covid: Level of coronavirus could be same between unvaccinated and double jabbed, study suggests

The level of coronavirus in people who have been double jabbed could be just as high as in those who remain unvaccinated, a study has suggested.

In preliminary research, which is yet to be peer reviewed, scientists from the University of Oxford found those infected with the Delta variant after their second jab had similar peak levels of virus to unvaccinated people.

But the study also showed that having two Covid vaccine doses is still the best way to protect against the Delta variant, first identified in India and now dominant in the UK.

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It found two doses of the Pfizer/BioNTech vaccine had a greater effectiveness initially against new Covid-19 infections associated with this variant when compared to the Oxford/AstraZeneca jab.

Though initially less effective, the Oxford/AstraZeneca jab offers the same high protection as the Pfizer/BioNTech after four to five months, the researchers concluded.

Sarah Walker, professor of medical statistics and epidemiology at the University of Oxford, said: “We don’t yet know how much transmission can happen from people who get Covid-19 after being vaccinated – for example, they may have high levels of virus for shorter periods of time.

“But 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.

“This means it is essential for as many people as possible to get vaccinated – both in the UK and worldwide.”

The study, conducted in partnership with the Office of National Statistics and the Department for Health and Social Care, looked at data between December 2020 and August 2021 from the Covid-19 Infection Survey.

Swab tests from more than 700,000 participants were analysed from before and after May 17 2021, when Delta became the main variant in the UK.

Analysis revealed that for infections with a high viral load, protection a month after the second Pfizer dose was 90% greater than an unvaccinated individual, reducing to 85% after two months and 78% after three.

For AstraZeneca, the equivalent protection was 67%, 65% and 61%, the researchers said.

NHS officials have geared up to start offering a third coronavirus jab from early September, but are yet to be given the green light to press ahead from the JCVI.