Elderly Britons who have received the AstraZeneca vaccine are less likely to have Covid antibodies than those who have received those from Pfizer, a study suggested.
Experts at Imperial College London found that less than 85% of those over 80 had detectable levels of anti-virus proteins two weeks after their second AZ jab.
In contrast, the proportion over the age of 80 with antibodies after receiving the second Pfizer vaccine was almost 98%.
The results come from Britain’s largest surveillance study, known as REACT-2, which randomly tests blood samples from hundreds of thousands of Britons.
Although antibodies are only part of the overall immune response to Covid, experts said they weren’t entirely surprising.
Professor Ian Jones, a virologist at the University of Reading, told MailOnline that the British jab was less likely to trigger immunity because it relied on a weakened cold virus.
In some cases, the body can attack this virus instead of the Covid proteins on its surface, so the jab does not trigger Covid immunity, he said. But Pfizer’s jab doesn’t have that problem because it uses completely different technology.
In jab trials, AstraZeneca’s vaccine was also found to be slightly weaker in preventing symptomatic Covid infection.
But a real-world analysis of the vaccine rollout in Britain has shown that both vaccines are extremely effective in stopping serious illness and death.
Even against the Indian variant, both have been shown to reduce the risk of being hospitalized with the virus by over 90%.
Britain’s largest Covid antibody study suggests Pfizer’s jab is more likely to trigger immunity to the virus than AstraZeneca’s. Experts said it’s because the Oxford-made jab is based on a weakened cold virus
REACT-2 has screened more than 207,000 participants from across the country for anti-Covid antibodies.
The study was conducted in the two weeks leading up to May 25, when the vaccination campaign had only just opened to people in their 30s.
Some people in younger age groups will have been vaccinated if they were in a priority group, including healthcare workers and those who were clinically vulnerable to the virus due to an underlying disease.
British health chiefs quietly warn Pfizer and Moderna’s vaccines could cause heart damage
British health chiefs quietly issued a warning that Pfizer and Moderna’s Covid vaccines could cause heart damage, MailOnline revealed last week.
Fears about the links between mRNA injections and myocarditis have increased in recent weeks, following a series of cases in young adults and children in Israel and the United States.
Now the UK’s medication watchdog has updated its safety information to accept that the disease is a possible side effect of both vaccines, without formal announcement.
The Medicines and Health Products Regulatory Agency insists that the complication – inflammation of the heart muscle that can damage the organ over time – is still “extremely rare” and “generally mild.”
But it wasn’t listed as a potential side effect until last week, when the MHRA released its most recent safety monitoring data.
Cardiologists say the benefits of both injections still clearly outweigh the risks for the vast majority of the population.
However, they say it “completely changes” the debate over childhood immunizations in Britain. They will not get the AstraZeneca vaccine because of its links to fatal blood clots in young people.
The study found that 100% of those under 39 who received AstraZeneca injections had antibodies two weeks after receiving their second dose.
This figure declined slightly among those 40 to 49 (99.4%), 50 to 59 (93.8%) and 60 to 69 (92.1%).
But it fell below nine in ten for those over 80 (83.6 percent).
By comparison, the Pfizer vaccine elicited protection in 100% of all age groups except those over 80, where the proportion was 97.8%.
But Professor Jones told MailOnline: “What seems true from these numbers – and this is one of the biggest surveys – is that the failure rate is higher for AstraZeneca than it is for Pfizer.
“There are individuals by chance or because of a recent cold who have antibodies against (the adenovirus) and who prevent it from entering [the immune system] in the first place.
Antibodies are only part of the immune response to Covid and do not determine how well a person is protected – for example, white blood cells also play a crucial role.
But they’re one of the main ways scientists can measure how well a person responds to a vaccine.
Antibody levels decrease over time, but that doesn’t mean they lose their immunity. The body stores memory of how to fight a specific virus long after the initial immune antibodies have fallen.
Johnson and Johnson’s single dose Covid vaccine also uses adenovirus technology. This vaccine has been approved in the UK and doses are expected to arrive in the fall.
Adenovirus vaccines work by using a weakened form of the common cold that delivers instructions to cells teaching them to fight Covid.
When the vaccine is administered, the patient’s immune system attacks the spike protein by creating antibodies, preparing it to fight Covid before it leads to infection.
Moderna jab, the third vaccine currently being deployed in Britain, is based on the same mRNA technology as that of Pfizer, which uses a synthetic delivery method.
Meanwhile, REACT-2 also discovered that black Britons were the group least likely to receive a Covid vaccine.
When their study was broken down by ethnicity, it found that antibody levels were 59% lower in black Britons compared to white Britons.
The NHS and ministers have led a campaign to make sure everyone is vaccinated against the virus, opening injection clinics at community centers and asking local leaders to call on their communities to get vaccinated.
The study also found that 61% of adults in the UK had antibodies in May, up from 13.9% in the two weeks to February 8.
But they said the levels were now probably “much higher” as more people were vaccinated.
Figures from the Department of Health show 46 million Britons received at least one dose of the Covid vaccine – 87.3% of adults – and 35.1 million received both doses – 66.6%.