Should People on Blood Thinners Avoid The COVID Vaccine?

Can people with blood thinners safely take Covaxin and Covishield?

4 min read

Considerable confusion has been caused by the statement related to ‘blood thinners’ in the product factsheet of Covaxin. It advises that persons who are on blood thinners should not take the vaccine.

Covishield’s fact sheet does not interdict vaccine administration on these grounds but advises persons to inform the healthcare provider if they are on blood thinners. These advisories have raised questions on what exactly are these drugs that constitute a barrier to vaccine administration as well as on the scientific rationale for that listed contraindication.

The Term ‘Blood Thinner’ Should Be Used Carefully

‘Blood thinner’ is a lay person’s term and should not have been used in the product information sheet, without specifying what kinds of drugs constitute contraindications to vaccination. It is a misleading term because the drugs usually grouped under this term do not dilute the blood like severe anaemia does.

However, 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.

Types of Blood Thinners

The drugs usually grouped under this term are of two types – anti-platelet drugs and anticoagulants. The former act against blood cells called platelets which can clump together to initiate the formation of a thrombus or clot. Anticoagulants are drugs which interfere with the action of proteins called coagulation factors that are involved in a cascade of reactions that end in a fibrin clot. Either way, the blood supply to vital organs can get cut off by the clots under conditions of disease, through these pathways are usually meant to be protective. In normal health. 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

Examples of anti-platelet drugs are 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.

Anticoagulants include heparin, warfarin, acenocoumarol, rivaroxaban, dabigatran, enoxaparin, apixaban, edoxaban and fondaparinux. Different anticoagulants 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.

People Prescribed With Anticoagulant Drugs Are At High Risk of COVID-19

Persons with any of the above medical conditions, for which anti-platelet or anticoagulant drugs are prescribed, are at a high risk of severe disease or even death if they are infected with the COVID-19 virus. They are among the people who will most need the protection of the vaccine. Why then are they listed as persons who should not receive the vaccine? Do these instructions apply to both anti-platelet drugs and anticoagulants?

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.

Persons with rheumatic heart disease, many of them young and thin, are required to take an intramuscular injection of long acting benzathine penicillin once in three to four weeks, to prevent streptococcal throat infection which may lead to recurrence of rheumatic fever and aggravation of heart disease.


If they have a mechanical heart valve implanted, they are on anticoagulants regularly, to prevent the valve from clotting. Anticoagulant medication is not stopped every time they get an intramuscular injection. What then is the rationale for stopping the persons who need it most and will benefit best from getting the vaccine?

Usually, any tendency to excessive bleeding due to anti-platelet or anticoagulant drugs would have already been detected and corrected through dose adjustment by the treating physician. No special tests are needed for monitoring anti-platelet drugs.

Anticoagulant 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.

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 anti-platelet drugs than with anticoagulants.


In either situation, there is no rationale for flat denial of the vaccine to those who need it most because of their medical conditions. Unless suitable clarifications are issued by the authorities, vaccinators may turn away persons who are on these drugs. It will be a disservice if many millions who are on aspirin because of cardiovascular risk are denied a potentially life saving vaccine. Can these instructions now flow through the fine needle of rational guidelines rather than the blunt rejection of all persons who are on ‘blood thinners’?

(Prof K Srinath Reddy, a cardiologist and epidemiologist, is President, Public Health Foundation of India (PHFI). He is the author of ‘Make Health in India: Reaching a Billion Plus’. The views expressed are personal).

(The article was first published in FIT and has been republished with permission)

(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 Member
Read More