Scientists compared rates of thrombosis among more than 1.3million recipients of either jab in Spain.
Both vaccines came with a tiny risk of causing blood clots, with scientists branding their safety profiles ‘broadly similar’. Pfizer’s jab may even be more likely to trigger the rare blood-clotting complication, the data suggested.
In contrast, the virus itself was eight times more likely to lead to thromboembolism than either jab.
The findings go against an array of research saying the opposite, with health chiefs yet to uncover a link between Pfizer’s vaccine and blood clots.
Safety concerns over AstraZeneca’s jab first emerged in January, and prompted EU nations to shun the British-made vaccine en masse.
Top scientists insisted the jab was safe and would save thousands of lives, leading to claims the bloc heavyweights were using the vaccine to play post-Brexit politics.
In light of the new findings, one UK Government official accused European leaders of having ‘blood on their hands’ for trashing the life-saving jab.
The experts noted the difference between the levels of conditions they expected to see (squares) in the general population and compared this to the cases they observed (circles) in people who received a vaccine or who caught Covid. The biggest change was seen among people who caught Covid, with the risk of developing a blood clot in the vein – called venous thromboembolism – jumping from from 62 to 499
Scientists noted that the different ages and health conditions of people who were given the Pfizer and AstraZeneca vaccine may have affected their findings. Of the 945,941 people who received one Pfizer jab (left), the average age was 75, while the 778,534 people fully immunised with Pfizer (middle) were aged 77 on average. But those who got one dose of AstraZeneca had an average age of 61 (right). The study was conducted in Spain, where national guidelines issued in March restricted the use of the Oxford jab to people in their 60s
The unnamed Whitehall insider told Politico: ‘We now know what we all suspected is true, they did it out of spite for Britain because of Brexit.
‘When the history books are written, they’ll say these people were directly responsible for the deaths of thousands in developing countries who won’t take AZ because of their anti-vaxx scare stories.’
Pfizer and Moderna Covid vaccines linked to very rare heart condition
British health chiefs have warned Pfizer and Moderna’s coronavirus vaccines may cause heart damage.
Since the vaccine rollout has been expanded to children in countries including the US and Israel, there have been reports of an extremely rare reported cases of myocarditis and pericarditis.
Myocarditis is inflammation of the heart muscle, while pericarditis is when the protective layer around the heart gets inflamed.
There are no specific causes of the conditions but they are usually triggered by a virus.
The UK is expected to wait for more data from clinical trials and other countries immunising children before making a decision to offer all youngster the jab.
The US, Israel and France are already giving the vaccine to over-12s.
Earlier this month, vaccines minister Nadhim Zahawi said the government had concerns about ‘very rare’ cases of heart inflammation in young people following the virus.
The Medicines and Healthcare products Regulatory Agency insists the complication – inflammation of the heart muscle which can damage the organ over time – is still ‘extremely rare’ and ‘typically mild’.
Data from the US — where cases of myocarditis have been spotted — suggests the complication is most common in boys and young men.
Covid vaccines have drastically slashed the risk of severe illness, hospitalisation and death from the virus.
Their rapid roll-out has allowed Britain to remove most remaining lockdown-esque restrictions, with ministers confident in how well they work.
But they have been linked to extremely rare complications, with AstraZeneca’s jab thought to cause blood clots in 11 in every 100,000 recipients.
Johnson & Johnson’s single-dose jab — which works in a very similar way — has also been linked to the same complication.
However, regulators have not spotted any consistent trend between Pfizer’s mRNA vaccine and blood clots. Its jab — linked to a very rare kind of heart inflammation — is based on pioneering technology.
Several countries in Europe stopped using the Oxford-designed AstraZeneca jab in March after a series of blood clots, with younger people facing a slightly higher risk.
Regulators analysed the data and found benefits vastly outweighed the risk for most.
But in the absence of doubt, UK health chiefs opted against routinely offering the jab to under-40s, who face a vanishingly rare risk of dying from Covid.
Since findings first emerged, there has been concern about the vaccine and its side effects, which experts fear has fuelled hesitancy among some groups in the UK and overseas.
The study, soon to be published in The Lancet, only looked at data from Catalonia — one region of Spain.
Independent scientists have yet to scrutinise the findings through a process known as peer-review, meaning the data remains unverified.
Researchers from the Foundation University Institute for Primary Health Care Research in Barcelona were behind the study, which also involved a team from Oxford and the Netherlands.
They compared rates of three different types of blood-clotting events among 1.3million people jabbed with either Pfizer or AstraZeneca.
Data was then compared to a control group of 4.5million people, to work out how whether the events were happening any more often than expected.
And the team, led by Ed Burn, a researcher associate in real world health economics at the University of Oxford, also looked at the medical records of 220,000 patients who had also had Covid, which is known to increase the risk of clots.
Results showed 211 people given a first dose of Pfizer developed blood clots in the veins or lungs, known as deep vein thrombosis and pulmonary embolism.
For comparison, the scientists — who received funding off the European Medicines Agency — calculated the background rate to be 169 in the general population.
This equates to a 25 per cent increase among Pfizer recipients, based on the researchers figures.
They saw slightly more blood clot cases in people who got AstraZeneca’s (39 cases compared to 35) but the overall risk was lower than from Pfizer’s.
Experts expected to see less cases among those receiving the Oxford vaccine, because the number of participants who received that jab was less.
They found this equated to a 20 per cent risk among AstraZeneca recipients of getting blood clots in the veins.
The Pfizer jab was not linked to blood clots with second doses, while the study did not examine people who got a second dose of AstraZeneca.
Risk of blood clots in the arteries — which are more serious — were similar between both jabs and lower than the rates experts expected to see.
Meanwhile, the risk of suffering the exact complication that spooked health chiefs around the world was low among both AstraZeneca and Pfizer recipients.
Scientists found both the AstraZeneca vaccine (right) and Pfizer (left) came with a tiny risk of causing blood clots, with scientists branding their safety profiles ‘broadly similar’. Pfizer’s jab may even be more likely to trigger the rare blood-clotting complication, the data suggested
The side effect — clots occurring alongside low platelet levels (thrombocytopenia) —occurred nine times in people who had the Pfizer jab when 20 were expected.
Meanwhile less than five cases were recorded in those who had the Oxford jab, so researchers could not draw a conclusion.
The risk of developing a blood clot in the vein alongside thrombocytopenia was four times higher from Covid.
And overall, the risk of clots was up to eight times higher from coronavirus than the two vaccines.
The experts noted that the participants included in the study may have swayed the result, with those who received the Pfizer jab were on average in their mid-70s.
Meanwhile, those who received AstraZeneca had an average age of 61.
The prevalence of health conditions that raise the risk of clots in the Pfizer cohort was also much higher.
Professor Kevin McConway, an emeritus professor of applied statistics at the Open University, said the findings on thrombocytopenia ‘aren’t very conclusive because the condition is so rare’.
Additionally, some of the differences between the groups who received the Oxford and Pfizer jabs ‘are pretty large’, including underlying health conditions and age, because national recommendations changed earlier this year.
All of the participants were based in Spain, which changed its policy towards the the rollout of the AstraZeneca jab.
Initially the Oxford vaccine was restricted to essential workers under 55, but after safety concerns emerged, this was restricted to just 60 to 65-year-olds, before being for all people in their 60s.
Professor McConway said: ‘These differences could, in part or in whole, be the cause of any increased risk on blood clotting in vaccinated people, or any differences between the two vaccines.
‘This means that the study cannot tell us whether any differences, or lack of differences, between people using the two vaccines or between vaccinated people and the general population, are actually caused by the vaccines. They might be, but they might not.’