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Newsroom: ISTH News

ISTH Statement on AstraZeneca COVID-19 Vaccine and Thrombosis

Friday, March 12, 2021  
Posted by: Andy Masten
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CHAPEL HILL, NC, USA, (March 12, 2021) - The International Society on Thrombosis and Haemostasis (ISTH) recommends that all eligible adults continue to receive their COVID-19 vaccinations, despite the recent decisions by Denmark, Norway and Iceland to at least temporarily suspend the use of the AstraZeneca vaccine due to reports of thrombosis.

At this time, the small number of reported thrombotic events relative to the millions of administered COVID-19 vaccinations does not suggest a direct link. Thrombotic events are common in the general population and have not previously been associated with vaccination. At present, we do not know whether the timing of the blood clots with vaccination is coincidental or whether vaccination may in rare cases increase the risk of thrombosis. Importantly, well-conducted clinical trials of COVID-19 vaccinations did not identify an increased risk of thrombosis.

Based on all available data, the ISTH believes that the benefits of COVID-19 vaccination strongly outweigh any potential complications even for patients with a history of blood clots or for those taking blood thinning medications. It also recommends that everyone review the signs and symptoms of blood clots, including: leg pain, swelling, tenderness or redness of the skin associated with deep vein thrombosis (DVT); as well as difficulty breathing, chest pain or discomfort, faster than normal or irregular heartbeat, coughing up blood and low blood pressure, light-headedness or fainting associated with pulmonary embolism (PE). Individuals with co-existing medical conditions may wish to consult their physician.

What does this mean for the patient community?

Based on currently available data, the ISTH believes that the benefits of COVID-19 vaccination   strongly outweigh any potential complications and recommends vaccination of all eligible adults.

The COVID-19 vaccine is given as an injection into the upper arm (intramuscular). Individuals taking direct oral anticoagulation (apixaban, dabigatran, edoxaban and rivaroxaban), warfarin in therapeutic INR range, full dose heparin or fondaparinux injections can all receive the COVID-19 vaccination. Vaccinating prior to the next dose of anticoagulant may be considered rather than immediately after taking the blood thinner.

  • There is a risk of bruising at the injection site, but serious effects related to anticoagulation are not anticipated  
  • Prolonged pressure (for at least 5 minutes) should be applied to the injection site to reduce bruising 
  • Patients on warfarin with supra-therapeutic INR should wait until their INR is <4.0 
  • We encourage patients to proceed with vaccination, which should not be avoided on the basis of anticoagulation 

If there are any questions or concerns, individuals are urged to contact their health care provider.

The ISTH COVID-19 Response Task Force, represented by an international committee of medical leaders, made these recommendations following their meeting on March 11, 2021.

EDIT: A previous version of this release listed Austria as a country that had suspended the use of the AstraZeneca vaccine. Authorities only suspended the use of one batch. 


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