THE COVID vaccines are preventing hospitalisations and deaths – but for how long are you protected?
A new study from Oxford University has attempted to answer that question.
With the majority of the UK adult population vaccinated, the findings also help answer whether a booster campaign will be needed.
Boosters are ready to be rolled out from September, should the Government decide to use them.
The study, which has not yet been peer-reviewed, looked at 700,000 people who did swab tests as part of the Covid-19 Infection Survey.
The analysis took place before and after the Delta variant, first seen in India, became dominant in the UK, so that researchers could assess the effectiveness of jabs against it.
Which vaccine lasts the longest?
Two doses of the Pfizer vaccine appear to have greater effectiveness initially against the Delta variant when compared to the AstraZeneca jab.
But its efficacy also declines faster, the preliminary research suggests.
Protection from infection a month after getting the second Pfizer dose was 90 per cent greater than an unvaccinated person.
It reduces to 85 per cent after two months and 78 per cent after three.
For AstraZeneca, the equivalent protection was 67 per cent, 65 per cent and 61 per cent, the researchers said.
Therefore, scientists said that after four to five months, the vaccines offer similar defence against Delta infection.
But the AstraZeneca jab maintained its effectiveness throughout.
A single dose of the Moderna vaccine had similar or greater effectiveness against the Delta variant as other jabs.
But the researchers added that they did not yet have any data on second doses of the US-made jab.
Research can't offer more information about how long the jabs work until people have had them for longer, as they only started being rolled out in December 2020.
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.
Dr Koen Pouwels, senior researcher at the University of Oxford’s Nuffield Department of Population Health, said that the team “can be confident” that the numbers “really represent a decline” for the Pfizer vaccine.
But he added: “Even with these slight declines in protection against all infections and infections with high viral burden, it’s important to note that overall effectiveness is still very high because we were starting at such a high level of protection.
“It is also worth highlighting that these data here do not tell us about protection levels against severe disease and hospitalisation, which are two very important factors when looking at how well the vaccines are working.”
Commenting on the research, Dr Alexander Edwards, associate professor in Biomedical Technology at the University of Reading, who was not involved in the study, said: “Overall this study is excellent as it shows that although Delta is better at infecting vaccinated people than previous variants, the vaccines still work remarkably well.
“There are subtle differences – between different vaccine types, and some changes over time – but they all work brilliantly.”
How much does your jab protect against Delta?
The study’s main findings were that the jabs work well against the Delta variant, first seen in India and now dominant in the UK, but not as well.
Two doses offer about the same level of protection as natural infection.
Although protection is lower than it was for the Alpha (Kent) version of the virus from the winter, a single dose still stops around half of cases.
Previous research from Public Health England has revealed two doses of Pfizer or AstraZeneca give more than 90 per cent protection against hospitalisation with Delta Covid disease.
The jabs have also been shown to provide 79 per cent (Pfizer) and 60 per cent protection against catching the Delta variant.
What else did the study find?
The Oxford findings also suggest younger people (aged 18-34) had more protection from vaccination than older groups (35 to 64-year-olds).
Vaccinated people infected with Delta have similar peak levels of virus to unvaccinated people.
This supports other research, suggesting that if a person with two doses catches Delta, they may be just as likely to pass it on to others.
Sarah Walker, professor of medical statistics and epidemiology at the University of Oxford, said: "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."
The study also found those who get Covid despite being vaccinated are no less likely to show symptoms than unjabbed, which goes against studies that have said cases are milder in those with a vaccine.
"What doesn’t seem to be out there is them ending up in hospital — so there’s a definite disconnect there," Prof Walker said.
She added: “This means it is essential for as many people as possible to get vaccinated – both in the UK and worldwide.”
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