AstraZeneca & Blood Clotting: All You Need to Know 

AstraZeneca & Blood Clotting: All You Need to Know 

Growing worries about blood clotting and the Oxford-AstraZeneca COVID-19 vaccine can add to vaccine hesitancy and hinder vaccination processes as cases surge in India.

What the EMA Found

The European Medicines Agency (EMA) confirmed that the cases of blood clots with low blood platelets were associated with the administration of the AstraZeneca Covid-19 vaccine, but should still be listed as very rare side effects.

In its latest assessment, EMA experts confirmed a probable causal link between extremely rare blood clots and the Oxford-AstraZeneca jab, but they added that the overall benefits of the vaccine in preventing Covid-19 outweigh the risks of side effects.

EMA's Pharmacovigilance Risk Assessment Committee made the conclusion after carrying out an in-depth review of the more than 80 cases reported in the European Union (EU) database.

A causal link between the AstraZeneca Covid-19 vaccine and the rare occurrence of blood clots with low platelets is "considered plausible but not confirmed," the World Health Organization (WHO) said, reported IANS.

According to the WHO’s statistics, as of Wednesday, 7 April, at least 2.6 million people have died of Covid-19 worldwide.

In an interim statement on Wednesday, 7 April, the WHO's Global Advisory Committee on Vaccine Safety (GACVS) said that the events under assessment are very rare, with low numbers reported among the almost 200 million individuals who have received the AstraZeneca vaccine around the world, Xinhua news agency reported.

However, specialized studies are needed to fully understand the potential link, and the GACVS said it will continue to gather and review further data.

Is the Vaccine Safe for Younger People?

The British government's vaccination advisory body said that Britons aged 18-29 will be offered an alternative to the Oxford-AstraZeneca vaccine in light of this news.

The Medicines and Healthcare products Regulatory Agency (MHRA) said the side-effects of the AstraZeneca vaccine were extremely rare and the vaccine's effectiveness is proven, adding that the benefits of taking the vaccine are still very favourable for the vast majority.

However, it conceded the new approach is more finely balanced for younger people because the risk from coronavirus is much lower.

Earlier, CTVnews reported that Canada’s National Advisory Committee on Immunization (NACI) has recommended pausing giving the jab to those under 55 years due to fears of recipients getting a rare type of blood clot called vaccine-induced prothrombotic immune thrombocytopenia (VIPIT).

Very Rare Side-Effects

June Raine, chief executive of the MHRA, said at a press briefing that, "This is extremely rare and the balance of benefits and known risks of the vaccine is still very favourable for the vast number of people.” She said the risk of this kind of side effect was about four in one million to those who receive the vaccine.

Is the Vaccine is Safe?

In a word: yes, say experts.

All vaccines have been approved post safety trials. Now, while clinical trials allow the scientists to assess relatively common effects, rare side effects can only be identified when vaccines are used at scale, says Raine.

"The evidence is firming up" but "more work is needed to establish beyond all doubt" the vaccine has caused extremely rare blood clots, she added.

GACVS added that rare adverse events following immunizations should be assessed against the risk of deaths from Covid-19 and the potential of the vaccines to prevent infections and reduce deaths.

Several European countries have already halted or suspended the rollout of the AstraZeneca vaccine in view of the reported risks - and as cases surge, this would halt the vaccination process and add to hesitancy. While it is understandable to be wary, experts assert that the side effects are incredibly rare and the benefits outweigh the risks.

Like virologist Dr Jameel said in an earlier FIT article, “The vaccine helps prevent severe infection and death, and so must be taken to fight the pandemic.”

Still, the scepticism is understandable - so let’s tackle vaccine hesitancy by explaining the facts.

What is Happening with the Blood Clots?

To understand the worries around the latest developments, let’s break down what’s gong on with blood clotting.

As per WebMD, a clot is “a clump of cells and protein in your blood that can help slow bleeding when you’re injured. It usually dissolves as you heal. But if it doesn’t, or if it forms when it’s not needed, it can clog up or completely block a blood vessel.”

They can cause severe problems like heart attacks and strokes.

AstraZenenca and Clotting

Till 24 March, the MHRA received 22 reports of cerebral venous sinus thrombosis (CVST) – a type of blood clot near the brain – and eight reports of other thrombosis events with low platelets, out of a total of 18.1 million doses of the jab, reported iNews.

A thrombosis is what occurs when a clot blocks a blood vessel.


As pere NHS, symptoms include:

  • Throbbing or cramping pain, swelling, redness and warmth in a leg or arm
  • Sudden breathlessness, sharp chest pain (may be worse when you breathe in) and a cough or coughing up blood

Symptoms of CSVT include:

  • A high temperature of 38ºC or above
  • Vomiting
  • Seizures (fits)
  • Changes in mental state, such as feeling very confused
  • A sharp and severe headache, particularly around the eye
  • Swelling and bulging of the eye(s) and the surrounding tissues
  • Eye pain that’s often severe
  • Double vision

An important point with the AstraZeneca jab and blood clots is that low levels of platelets and rare antibodies being reported in the blood.

This is what indicated to a causal link between the jab and the clotting.

Covishield and Clotting

In India, Covishield is shown to be 63 per cent effective in ongoing, large-scale clinical trials based on data provided by the manufacturer. A vaccine can help if in a pandemic if it is more than 50 per cent effective.

Adar Poonwalla, CEO of Serum Institute of India, has said that the efficacy of Covishield rises to as much as 90 per cent if the two shots are separated by about 2.5-3 months.

The benefits of the vaccine outweigh the risks, especially when there is high transmission and rising cases say experts.

(At The Quint, we are answerable only to our audience. Play an active role in shaping our journalism by becoming a member. Because the truth is worth it.)

Speaking truth to power requires allies like you.
Become a Quint Insider

or more


3 months
12 months
12 months
Check Insider Benefits
Stay Updated

Subscribe To Our Daily Newsletter And Get News Delivered Straight To Your Inbox.

Join over 120,000 subscribers!