Blood Clotting & COVID: AstraZeneca Pause in EU Nations Explained

What is the link between blood thinners and the AstraZeneca COVID vaccine? Why has the EU suspended it?

Health News
6 min read
Blood Clotting & COVID: AstraZeneca Pause in EU Nations Explained

On Thursday, 11 March, Norway, Denmark and some other European countries suspended the use of the Oxford-AstraZeneca COVID vaccine post reports of blood clotting in some vaccine recipients. There were also reports that a 50-year-old man had died in Italy after developing deep vein thrombosis (DVT) following a dose of the jab.

However, the EU's medicines regulator said that there is no indication that the vaccine is linked to an increased risk of blood clots, reported IANS. It said the number of cases in vaccinated people was no higher than in the general population.

“There is currently no indication that vaccination has caused these conditions, which are not listed as side effects with this vaccine. The vaccine’s benefits continue to outweigh its risks and the vaccine can continue to be administered while investigation of cases of thromboembolic events is ongoing,”
European Medicines Agency (EMA) said on Thursday, 11 March.

It said there had been 30 cases of "thromboembolic events" among the five million Europeans who have received the jab.

On Friday, 12 March, the World Health Organisation also released a statement saying there was no need to stop the vaccine over blood clot fears.

“Yes, we should continue using the AstraZeneca vaccine. There is no indication to not use it”.
Margaret Harris, WHO spokesperson told reporters

AstraZeneca said the drug's safety had been studied extensively in clinical trials. "Regulators have clear and stringent efficacy and safety standards for the approval of any new medicine," a spokesperson said.

Should You Worry?

Recently there was much confusion about blood thinners in India as well, with the ICMR ultimately saying there was no need to worry, and it was safe to take the vaccine for all (after consulting a doctor first).

Why has this become an issue in the EU? Should India, which manufactures the same vaccine, be worried?

Fortis cardiologist Dr Pramod Kumar clarifies, “The worries over blood thinners in India and Europe are very different. Here, no one should worry and all should take the vaccine if it’s available to you.”

So what is the problem?

“In Europe, the vaccine was stopped as a precautionary measure. The blood became thick and a 50-year-old died post taking the jab although a link was not found. In fact, the regulatory body said there was no scientific link between the two incidents.”

Italy's medicines body said its decision was "precautionary", adding that no link had been established between the vaccine and subsequent "serious adverse events".

So far, Denmark, Norway and Iceland have temporarily suspended the rollout of the AstraZeneca vaccine. Italy and Austria, meanwhile, have stopped using certain batches of the drug as a precautionary measure. The suspensions in Italy and Austria involve different batches of the vaccine. Estonia, Latvia, Lithuania and Luxembourg have also suspended the use of the same batch as Austria.

Dr Kumar explains that the problem seems to be with a particular batch, ABV 5300 - the same that has been stopped in the aforementioned countries.

“Right now, they are collecting and examining the batch. There could have been contamination which means the incident is not directly related to the vaccine. It could even be a coincidence.”

In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) said there was no evidence the vaccine had caused problems, and people should still go and get vaccinated when asked to do so. "Blood clots can occur naturally and are not uncommon. More than 11 million doses of the Covid-19 AstraZeneca vaccine have now been administered across the UK," said Phil Bryan of the MHRA.


India’s Rules for Blood Thinners & COVID Vaccines

In India, SII is manufacturing the Oxford-AstraZeneca vaccine as Covishield, so should we worry? “Here, we have given the same vaccine to almost 1.5 crore people and no one has reported any such case.”

On 30 January, 14 days after India started the vaccination drive, vaccine manufacturers Bharat Biotech and Serum Institute of India approached the drug regulator to allow the use of their vaccines - Covaxin and Covishield respectively - for people using blood thinners, said ICMR chief Balram Bhargava.

The fact sheets for both candidates mention the contradiction, and the companies want to change this point. Bhargava explained that of the two types, antiplatelets such as aspirin and clopidogrel, are not of concern at all.

“The second category is anticoagulants like heparan, and these patients have a tendency to bleed much higher. The only worry is, there can be local hematoma or swelling can occur where the injection site is. Therefore, it is a very relative contraindication. The anticoagulants can be stopped for one or two days before giving the vaccine.”
Balram Bhargava

“The ICMR has said that those within a therapeutic range of anticoagulation and those on antiplatelets do not have to worry,” says Dr Kumar.

Dr Srinath Reddy explains, “Anti-coagulant dosage is monitored by periodically performing a blood test for estimating INR (International Normalised Ratio) or PT (Prothrombin Time). These tests help to identify a dose that is both effective and safe.”

He adds, “According to Public Health England’s Green Book, a person on anticoagulant therapy can receive the Covid-19 vaccine, if the INR is below the upper level of the therapeutic range. It is recommended that the injection be made with a fine gauge needle (23 or 25 gauge) and firm pressure is applied to the injection site for two minutes. If there is doubt about the anticoagulant status, the person is referred to the treating physician for review and recommendation. Though no cautionary guidelines are prescribed for persons on anti-platelet drugs, similar precautions may be followed for them with respect to a fine needle and longer compression of the injection site. The risk of bleeding or haematoma is in any case less for antiplatelet drugs than with anti-coagulants.”

If you are above the recommended range and you take the COVID vaccine, you may experience bleeding in your muscles, explained Dr Kumar. “Talk to your doctors if you are worried, but the vaccine is safe for you.”

Understanding the Basics:

What Are Blood Thinners:

Dr Srinath Reddy said in a previous FIT article, “Blood thinner’ is a lay person’s term,” and there are many drugs that come under this category.

“They act to prevent or break up fresh blood clots in the blood vessels of the body or the heart itself. They can be best thought of as drugs slowing down or stopping the formation of blood clots.”
Dr Srinath Reddy

He adds, “The drugs usually grouped under this term are of two types - anti-platelet drugs and anticoagulants.”

1) Anti-Platelet:

  • Act against blood cells called platelets which can clump together to initiate the formation of a thrombus or clot.
  • Examples include aspirin, clopidogrel, dipyridamole, ticlopidine, prasugrel and eptifibatide. Many persons with known coronary heart disease or cerebrovascular disease are on either aspirin or clopidogrel or even both.
  • These oral drugs are also advised for persons with multiple risk factors which place them at high risk of heart attack or stroke. Persons with implanted stents in coronary arteries or other blood vessels are also prescribed anti-platelet drugs.

2) Anticoagulants:

  • Drugs that interfere with the action of proteins called coagulation factors that are involved in a cascade of reactions that end in a fibrin clot.
  • Examples include eparin, warfarin, acenocoumarol, rivaroxaban, dabigatran, enoxaparin, apixaban, edoxaban and fondaparinux.
  • Different anti-coagulants interfere with different coagulation factors. Persons with venous thrombosis, atrial fibrillation or mechanical heart valves are usually on one of these.
  • Some of these are injectable, while others can be taken as oral tablets.

In both ways, the blood supply to vital organs can get cut off by the clots under conditions of disease, though these pathways are usually meant to be protective. If they function inadequately, we would bleed excessively from cuts. If they are overactive, we will have clotting inside arteries, veins or in the chambers of the heart.

Blood Thinners & COVID

Now people with severe diseases like the ones mentioned above, who presumably take the drugs mentioned to control their diseases, are at a higher risk of severe infection or death by COVID.

So it makes sense that they might be most in need of the vaccine. So what is the link between blood thinners - of each type - and the COVID vaccine?

Dr Reddy says:

“Though no clear explanation has been forthcoming from the vaccine manufacturers, some doctors have attempted to explain the exclusion of persons on blood thinners as a needed precaution to prevent excessive bleeding or formation of a haematoma (blood collection causing a swelling in the muscle into which the injection is made). How justified is this fear? Millions of heart patients world over, who are on anti-platelet drugs, get influenza vaccine injections (‘flu shots’) frequently. Some of them get pneumococcal vaccine injections.”
Dr Srinath Reddy

Dr Kumar concurs, “The people on these are the ones who are prone to severe disease and hence need the vaccine.”

Vaccine Suspension During Rising Cases

The decision to temporarily suspend the use of AstraZeneca's jab has come as a setback for a European vaccination campaign that has stuttered into life, partly due to delays in delivery of the drug.


This also comes at a time when cases in Europe are rising again: Czech Republic, Hungary, Estonia, Slovakia, Italy, France, Poland and Sweden have seen significant rises in average new daily cases recently. The New York Times reported that the EU has recorded over 800,000 new coronavirus cases over the past week, an increase of about 5.8% from the seven days prior. Most of the struggling countries are from central and eastern Europe.

(With inputs from IANS and The New York Times )

(This story was first published on Quint Fit)

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