May 16, 2021

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What are the risks of blood clots from AstraZeneca’s Covid vaccine REALLY?

British health chiefs have restricted AstraZeneca’s vaccine in under-30s because their risk of dying from Covid is so small and there are early signs they may be more prone to blood clots after the jab.

But EU regulators have decided against recommending the vaccine is withheld from any age group because they can’t be sure that young people are definitely most at risk of the extremely rare complication.

UK’s own medical watchdogs confusingly hold the same opinion but acknowledge cases of rare blood clots from the life-saving jab are occurring slightly more often in younger adults.

For this reason, the JCVI — No10’s vaccine advisory panel — has acted out of extreme caution to restrict the jab to under-30s because its benefits don’t clearly outweigh the risks in younger adults, who face a vanishingly small risk of falling seriously ill or dying from the disease.

EU nations have defied their own regulator’s guidance, with Belgium, Germany and Italy shunning the vaccine for under-60s.

But statistical analysis of the risks — done by Cambridge University academics and used to justify the UK’s ‘course correction’ in the roll-out — show the benefits of the jab are much clearer for over-30s, who face a slightly higher risk from the disease and appear to suffer fewer blood clots.

Scientists have still yet to prove the vaccine causes the blood clots and are struggling to untangle the risk factors because young people are also more at risk of suffering the clots. But experts say the evidence is shifting.

‘We felt that the benefits outweighed the risk in those above 30 years old. But in those under 30, the benefits and risk look more similar,’ said deputy chair of the JCVI Anthony Harnden.

In total, more fatal blood clots have developed in 30 to 39-year-olds than any other age group and more of them have been found in women than men.

But statistical analysis supporting the UK decision was done by eminent statistician Professor Sir David Spiegelhalter, who found that the clots were more common in even younger people. 

Professor Spiegelhalter said data suggested about one in 90,000 people aged 18 to 29 given the AstraZeneca jab will likely suffer the clots compared to one in 500,000 over-60s.

Highlighting how the benefit-risk balance of the AstraZeneca vaccine swings heavily in favour of even middle-aged people, his team’s calculations show people in their 40s are 100 times more likely to be hospitalised with Covid if they refuse jab.

Professor Spiegelhalter said the change in vaccine guidance had been made as precautionary measure because young people were being hit with a ‘double whammy’.

He told MailOnline: ‘There does seem to be extra risk in younger people of getting this combination of quite really odd particular group of symptoms [brain clots and low platelet counts].

‘Younger people are also not benefiting so much from vaccine, so in sense they’re getting a double whammy. They are at a higher risk from the vaccine and lower benefit from the vaccine.’

Regulators in the EU, on the other hand, have decided against restricting the British-made vaccine’s use in any age group, claiming that age is not a risk factor.

Professor Spiegelhalter said he was ‘not sure’ how the European Medicines Agency could have come to such a different finding, reiterating that the ‘data definitely does show there is an age gradient.’ 

He admitted that Europe needed the AstraZeneca vaccine more than the UK because the continent is in the midst of battling a third wave and is struggling to get its jab rollout up to speed. 

This graphic shows the seating plan of Wembley Stadium which holds 90,000 people. If it were full and 10,000 people squeezed onto the pitch, there would be 100,000 people – the same number as Professor Spiegelhalter’s risk groups. If all of them were 20-29 and had the AstraZeneca jab, one would be expected to get a blood clot, top left. While if they were all 50-59, no blood clots would be expected. The panels on the right show the risk of serious Covid if they all refused the vaccine 

The Government yesterday wheeled out a series of graphs comparing the risk of falling ill with Covid compared to the threat of developing blood clots after getting the AZ vaccine in various age groups. In low Covid levels, every 100,000 vaccines prevents 0.8 ICU admissions from coronavirus in people under 30 but 1.1 people will suffer blood clotting after having the jab, making the threat higher than the virus itself

The Government yesterday wheeled out a series of graphs comparing the risk of falling ill with Covid compared to the threat of developing blood clots after getting the AZ vaccine in various age groups. In low Covid levels, every 100,000 vaccines prevents 0.8 ICU admissions from coronavirus in people under 30 but 1.1 people will suffer blood clotting after having the jab, making the threat higher than the virus itself

But justifying their decision not to restrict the vaccine by age, Dr Sabine Strauss said: ‘Our review has shown that there is a predominance of these rare events of thrombosis combined with thrombocytopenia in certain groups – notably in women and younger women.

‘But it is still rather premature to conclude on a specific group because the background risk of thrombosis may be different in various groups and it may also be the case that more people have received this vaccine in certain groups in different countries. The potential for different risk levels is part of our further evaluations.’ 

The EMA and its UK equivalent, the MHRA, both say the AstraZeneca is safe for every age group, including the under-30s. The EMA has left it to individual countries to carry out their own risk-benefit analysis and decide whether to suspend the jab’s use, which has led to nations taking different approaches.

Germany has banned its use in under-60s, while France is not recommending it for under-55s. Britain’s JCVI said the benefit versus risk stopped at people aged 30 and below.

Putting the tiny risk of jab-related clots into context, Professor Spiegelhalter said if a cohort of people in their 20s large enough to fill Wembley Stadium was given the UK-made jab, just one person would likely develop clotting.

Professor Spiegelhalter added that he believes the low risk coronavirus directly poses to young people makes their decision to get vaccinated altruistic, because it stops them passing it to vulnerable people, has not been emphasised enough. 

It comes after the Joint Committee on Vaccination and Immunisation ruled yesterday that healthy Brits under 30 should be given an alternative to the AstraZeneca vaccine while experts probe the clot links.

Professor Spiegelhalter said the UK had the luxury of being able to pivot because it has plentiful vaccine supplies and low levels of Covid infection, which meant the relative risk of the clots was higher than the threat of the virus.

However, should there be a resurgence of Covid transmission or if the UK is hit with vaccine delivery issues, then the relative importance of the risk of blood clots would decrease.

When coronavirus is prevalent in society, 100,000 AstraZeneca vaccines prevent 127.7 Covid ICU admissions among 60 to 69-year-olds. For 20 to 29-year-olds, every 100,000 vaccine administered stops seven people in that age group from being admitted to intensive care with the disease

When coronavirus is prevalent in society, 100,000 AstraZeneca vaccines prevent 127.7 Covid ICU admissions among 60 to 69-year-olds. For 20 to 29-year-olds, every 100,000 vaccine administered stops seven people in that age group from being admitted to intensive care with the disease


MHRA data leaked to ITV shows that, in total, more fatal blood clots have developed in 30 to 39-year-olds than any other age group.

According to the regulator’s review, by March 31 there had been 79 cases of the side effect and 19 deaths.

The 79 cases occurred in 51 women and 28 men, aged from 18 to 79. 

Some 14 cases of the 19 were cerebral venous sinus thrombosis (CVST), a specific type of clot that prevents blood from draining from the brain.

The other five cases were thrombosis. An age breakdown of the cases is shown below: 

Age range

18 – 29

30 – 39

40 – 49 

50 – 59

60 – 69

70 – 79



The exact combination of symptoms affecting a small number of people given the AstraZeneca vaccine are so rare there is no reliable data, according to Professor David Speigelhalter.

But the MHRA has said CVST – the deadly brain clot found in many of the patients – normally occurs in five to 16 cases per million in the UK every year, according to LBC’s Ben Kentish.

The regulator said the condition, which occurs when a vein that drains blood from the brain is blocked by a clot, has been found in two cases per million in the three months since the vaccine rollout began.

In Europe, regulators  said they spotted 53 cases of splanchnic vein thrombosis (SVT), a type of clot in the liver, from 34million jabs.

It’s unclear if any vaccinated Brits have suffered from SVT, which is estimated to affect fewer than one per million people a year. 

Professor Spiegelhalter told the BBC Radio 4 Today programme: ‘It’s a complex message here because there is a balance of risk and the unfortunate pattern is that the younger someone is, the benefits [of the vaccine] get less, in terms of the direct benefits to your health. But the risks do increase somewhat of getting this very nasty side effect [clotting].

‘At some point it’s inevitable that balance will tip in some context. In the context we are in at the moment, where actually there’s not that much virus circulating, they’ve decided as guidance that for people under 30,  it has tipped in favour of an alternative vaccine. But in a different context if theres a lot more virus then that guidance would change.’

Slides presented at yesterday showed that, for 20 to 29-year-olds, every 100,000 AstraZeneca vaccine administered stops seven people in that age group from being admitted to intensive care with coronavirus.

However, in low Covid levels, every 100,000 vaccines prevents just 0.8 ICU admissions from coronavirus in under-30s. Whereas, 1.1 people per every 100,000 will suffer blood clotting after having the jab, making the risk of the clots higher than the virus itself.   

But Professor Spiegelhalter said the statistics do not account for the indirect benefits that vaccination offer to anyone those people came into contact with after getting their jab.

He added: ‘This is something that perhaps should have been emphasised all the time for younger people, who can get long Covid, and it would prevent the huge numbers of that as well, but [also] being vaccinated is as much a contribution to the community and their relatives and the people around them. Preventing transmission has this direct benefit for themselves.’   

The European medical regulator the EMA decided against restricting the AstraZeneca vaccine for any age group yesterday, saying that blood clots should be listed as a ‘very rare’ side effect. It doubled down on its message that the benefits far outweighed the small risk. 

It came as the sister of a married lawyer who died from a blood clot after receiving the AstraZeneca vaccine today joined the legion of politicians and health experts encouraging people to continue taking up the jab and said: ‘My brother was just extraordinarily unlucky’.

Neil Astles, 59, who lived in a £275,000 detached house in Newton-le-Willows on Merseyside, became the UK’s first named victim after passing away last weekend following 10 days of severe headaches and a steady loss of vision.

Mr Astles, who married his wife Carole in 1993 and worked as a council solicitor in nearby Warrington, died on Easter Sunday.

His sister Dr Alison Astles, a pharmacist at the University of Huddersfield, said her brother was a keen runner, was ‘fit and healthy’ and had no history of blood clots.

But he developed a headache about a week after his vaccination March 17. When his headaches and eyesight worsened, he was rushed to A&E at the Royal Liverpool Hospital by his brother, before being admitted to intensive care, where he died more than a fortnight later.

Dr Astles told the Daily Telegraph: ‘Despite what has happened to our family, we strongly believe that everyone should go for their first and second doses of the AstraZeneca vaccine. Emotionally, we are completely and utterly furious. We are suffering. But there’s nothing in our minds to be really furious about. My brother was just extraordinarily unlucky.’

Yesterday Britain’s medical regulator the MHRA announced the vaccine created by Oxford University and produced by AstraZeneca would not be used for those under 30 following extremely rare cases of clotting. Boris Johnson also declared the jab was safe and will save lives.

According to the MHRA the chance of suffering blood clots after receiving the AstraZeneca jab was 0.000095 per cent. The BMJ said the risk is the same as being killed by a plane falling from the sky and crashing on your house.

Dr Alison Astles agreed and said: ‘If we all have the vaccine, a few of us might have a blood clot but the evidence is that fewer people will die.’

But there are concerns public confidence will have been damaged by the change in policy, made worse by chaos in Europe where EU health ministers have failed to agree joint guidelines for who should be given AstraZeneca jabs as many nations reserved the use of the vaccine to the over-55s or over-60s while Germany has placed restrictions in all age groups.

The curbs came despite the head of the European Medicines Agency declaring there is ‘no evidence’ to support restricting the use of AstraZeneca’s coronavirus vaccine.

Is it safe for me to get my second dose of AstraZeneca’s vaccine if I had agonising headaches? Can I ‘mix and match’ to get Pfizer’s instead? All the answers to your questions about the jab’s link to blood clots 

AstraZeneca‘s coronavirus vaccine is once again under the spotlight, amid growing fears it may trigger extremely rare blood clots. 

Health chiefs yesterday recommended it should not be given to under-30s because of its link to the potentially deadly complication. 

But medical experts insist the jab is safe and the benefits far outweigh any risks for the majority of adults, with the overall risk of dying from a blood clot after getting jabbed being around one in a million. 

Here MailOnline answers all of your questions about what is really going on with the vaccine, revealing why you can’t ask to get a second dose of Pfizer‘s jab instead and why you should not be concerned by any link to blood clots. 



MHRA chief executive Dr June Raine said anyone who has one or more of the below symptoms for longer than four days after vaccination should seek urgent medical advice.  

  • Shortness of breath 
  • Chest pain 
  • Swollen legs 
  • Persistent stomach pain 
  • Severe headache 
  • Blurred vision 
  • Skin bruising beyond the site of injection

The Joint Committee on Vaccination and Immunisation — which advises ministers on the vaccination roll-out — says anyone who has already had their first jab should still get their second ‘irrespective of age’.

This is because the second dose ‘will be important for longer lasting protection against Covid’, the panel says. 

Only the handful of Brits who developed major blood clots occurring with low platelet levels after getting their first dose should avoid their second.

Everyone else should attend their second appointment as normal, regulators insist. 

No evidence currently exists to say there is any link between getting AstraZeneca’s top-up vaccine and getting potentially deadly blood clots. 

But anyone who suffered one of the tell-tale symptoms of the rare complication should still speak to their doctor before receiving their second dose, purely out of caution, advisers say. 

Severe headaches and blurred vision that last longer than four days after receiving the vaccine are two warning signs of the brain blood clot linked to AstraZeneca’s jab, called CVST.

But it has also been linked to blockages in other veins, which can cause swollen legs, bruising beyond the site of the jab, crippling abdominal or chest pain, and feeling short of breath. 

The JCVI insisted the clots ‘appear to be an idiosyncratic reaction on first exposure’ to AstraZeneca’s vaccine.

Officials have not recorded any cases of blood clots after a second dose, with all 79 incidents occurring after the first jab. 

Professor Adam Finn, of the JCVI, said facts could change but at the moment there is ‘no evidence of a problem after the second dose’.

‘At the moment we would be voyaging into an evidence-free zone if we recommend people do not have a second dose,’ he added. 



Very Common (may affect more than 1 in 10 people)

  • tenderness, pain, warmth, itching or bruising where the injection is given
  • generally feeling unwell
  • feeling tired (fatigue)
  • chills or feeling feverish
  • headache
  • feeling sick (nausea)
  • joint pain or muscle ache

Common (may affect up to 1 in 10 people)

  • swelling, redness or a lump at the injection site
  • fever
  • being sick (vomiting) or diarrhoea
  • flu-like symptoms, such as high temperature, sore throat, runny nose, cough and chills

Uncommon (may affect up to 1 in 100 people)

  • feeling dizzy
  • decreased appetite
  • abdominal pain
  • enlarged lymph nodes
  • excessive sweating, itchy skin or rash

Source: MHRA 

Brits who suffered flu-like symptoms after getting the first jab do not need to worry, experts say.

Side effects from vaccines are normal and go away on tend to disappear within 48 hours.

They are a sign they are working, with the side effects a result of the jab prompting the immune system to gear up to fight the virus.

Data shows one in ten recipients of the jab will feel unwell after their initial vaccine, or suffer fatigue and joint pain. 

The Medicines and Healthcare products Regulatory Agency (MHRA), which polices the safety of all the drugs, says headaches are also a very common side effect.

Officials say only vaccinated Britons who are struck down with crippling headaches four days after getting jabbed should seek medical help.

They say the headache may not be relieved with painkillers or feel worse when you lie down or bend over. The agony may also occur alongside blurred vision, vomiting, or speaking difficulties.  


Drug regulators have yet to approve a mix-and-match policy for jabs, meaning Brits who were given the AstraZeneca jab must stick with it. 

JCVI bosses have no reason to believe letting people receive Pfizer or Moderna’s jab the second time around would be dangerous. 

Professor Anthony Harnden, deputy chair of the advisory panel, told Good Morning Britain the safest thing to do at the moment ‘would be to receive the same type.’

He said: ‘This is an evidence free zone at the moment because all the trials have been done using the same vaccine.

‘There is work undergoing at the moment to use different vaccine types but we just don’t have that data and we don’t have the safety data on that.’ 

British scientists launched the world’s first trial at mix and matching Covid vaccines earlier this year. 

The study of 800 patients will look at the effect of giving someone an initial dose of the Oxford University jab, followed by the Pfizer one, and vice versa.

Scientists will trial other vaccine combinations as more are approved and rolled out across the UK over the course of the year-long research.  

Experts believe the ‘mix and match’ approach could stimulate different parts of the immune system and give better, longer lasting immunity.

The tactic could also help Britain deal with supply shortages which has held back the UK’s otherwise successful vaccination rollout. 


Only healthy under-30s are currently being offered the choice of whether they take AstraZeneca’s coronavirus vaccine.

But younger adults can still opt to take the jab, if they would like. 

The MHRA has not placed any legal age-restriction on the vaccine, with the decision made out of an abundance of caution.

Advisers argue because young people are at such low risk of becoming seriously ill with Covid, the benefits of the vaccine are not as clear-cut.

The JCVI says ‘the benefits of prompt vaccination with AstraZeneca’s Covid vaccine far outweigh the risk of adverse events’ over-30s and anyone with underlying health conditions that put them at higher risk of Covid.


More than 20million doses of the AstraZeneca vaccine have now been given in the UK, with the jab used as the main weapon in the UK’s arsenal.

The roll-out is unlikely to move on to under-30s for several weeks, meaning supplies of other jabs could be saved for younger adults.

Moderna’s jab was deployed in Britain for the first time today, with ministers having bought 17million doses — enough for 8.5million people.

The chief scientist behind the US-developed Novavax vaccine, which Britain has secured 60million doses of, has said he expects it to be given the green light this month and rolled out in May.

A separate vaccine made by American pharmaceutical giant Johnson and Johnson, which uses the same type of technology as AstraZeneca’s but is administered via a single injection, is slated for a summer rollout. No10 has bought 30million doses.

The UK has also ordered 40million Pfizer doses, enough for 20million people, but the majority of the country’s remaining stocks are reserved for second doses.

But, given that AstraZeneca’s vaccine is the main driver of the campaign, the roll-out could be slowed if the UK’s change of heart on giving the jab to young adults knocks public confidence in 30-50 year olds.


European health chiefs ruled that AstraZeneca’s jab should come with a warning that, in very rare cases, it may cause potentially deadly blood clots.

The EMA, which polices the safety of drugs used on the continent, spotted 169 cases of cerebral vein thrombosis (CVST) and 53 cases of splanchnic vein thrombosis (SVT), from 34million jabs.

CVST occurs when a vein that drains blood from the brain is blocked by a clot. It can lead to a stroke.

SVT is the same type of blood clot but it occurs in the digestive system.

Both the EMA and their UK counterparts said the clots had occurred alongside thrombocytopenia — low levels of blood platelets. 


CVST is where potentially fatal clots form in the veins that run from the brain. 

Unusually, this is occurring with thrombocytopenia – abnormally low levels of blood cells called platelets. 

Platelets cause blood to clot, so while not unheard of, it is incredibly rare for people with low levels to develop clots.  

The most severe signs of CVST include stroke-like symptoms such as weakness of the face and limbs on one side of the body, seizures, coma and ultimately death.

But anyone who has suffered headaches, blurred vision, shortness of breath, chest pain, leg swelling, abdominal pain and bruising or pinpoint spots below the vaccination site for four days after a jab should seek medical attention.


No cases of CVST with low platelets have been linked to the Pfizer vaccine in the UK, with just two serious clots reported more widely. 

Experts suggest this could be to do with the technology in mRNA vaccines, such as Pfizer and Moderna, compared to those using adenoviruses, for example, AstraZeneca and Johnson & Johnson.

Trials of the latter have shown possible clots, although scientists stressed they were incredibly rare with three reported cases in 4.5million jabs administered.

So far, only the Oxford jab has been linked to possible raised levels of clotting. All vaccines will continue to be monitored.


Figures presented by the EMA — which took into account data up until April 4 — suggested the clots occur once in every 150,000 jabs. They also said most of the cases were in women under 60.

The MHRA, which plays the same role in the UK, found 79 cases of clots in 20million doses by the end of March. Officials said the risk was around one in every 250,000 doses.

They also insisted the benefits of the vaccine outweigh the risks for the vast majority of people — but that the ratio was more ‘finely balanced’ in younger people, who are slightly more prone to blood clots.

LBC claimed that the MHRA revealed the baseline rate of CVST was between five and 16 cases per million people each year. The MHRA has spotted 44 cases of that blood clot — a rate of two cases per million people every three months.

EMA chiefs said that clots occurred more often than expected, prompting them to say the jabs need to come with the warning that it is a rare side effect.

But it said the committee investigating the link did not conclude that age and gender were clear risk factors for the very rare side effects.


Scientists are exploring several possibilities. 

European investigators have put forward one theory that the vaccine triggers an unusual antibody in some rare cases, similar to conditions seen in patients treated with the anticoagulant – commonly known as blood thinner – heparin. 

The autoimmune disorder called heparin-induced thrombocytopenia (HIT) leads to plummeting platelet counts and clotting.

Others are looking at whether the cases – which seem more common in women – are linked to birth control pills. 

However, at the moment scientists say there is no definitive evidence.  


The advice on this has not changed, meaning it’s recommended that those who are pregnant should not be vaccinated, with some exceptions. This is because the vaccines have not yet been tested in pregnancy.

While there is no evidence to suggest that the vaccine would harm the baby, pregnancy is more likely to lead to thrombosis.

Therefore women should discuss with their healthcare professional whether the benefits of having the vaccine outweigh the risks for them.


Officials say this will not happen unless you have an underlying medical condition and are prioritised. 

In such instances, they say the benefit of having the vaccine far outweighs any issues as you have an equivalent risk from coronavirus as 65 to 70-year-olds. 

For healthy under-30s, officials are confident there are sufficient supplies of the Pfizer and Moderna vaccines coming on stream to vaccinate all 10million 18 to 29-year-olds in the UK.


No. The risks of an adverse clotting event are extremely low. Taking aspirin or anti-coagulants can increase the risk of bleeding and is not