A history of blood clots is not a reason to avoid the AstraZeneca vaccine. we look after many patients who have had blood clots in the past or take blood thinners. They often ask: “should I have the AstraZeneca vaccine?”
The answer is usually a definitive “yes”. The blood clots we’ve seen following the AstraZeneca vaccine are completely different to other types of blood clots, such as deep vein thrombosis or a pulmonary embolism, or the clots that cause heart attacks and strokes.
People with a history of these sorts of conditions don’t appear to be at any increased risk from the AstraZeneca vaccine.
In fact, people in this group could be at greater risk from COVID-19, so shouldn’t delay getting vaccinated.
What is TTS?
The AstraZeneca vaccine is associated with a rare condition called thrombosis with thrombocytopenia syndrome, or TTS. Cases of the condition have also been reported following the Johnson & Johnson COVID vaccine, though this one isn’t available in Australia.
We now know a lot more about this condition than we did a few months ago.
TTS is caused by an abnormal immune response, resulting in the development of an antibody directed at the platelets (blood cells which prevent bleeding). This causes the platelets to become hyperactive, which triggers blood clots in the body, including in places we don’t normally see clots, like in the brain or the abdomen.
This process also consumes platelets, which results in a low platelet count. In the name “thrombosis” refers to clots, and “thrombocytopenia” to low platelet count.
Don’t delay getting the vaccine because of clots
As an immune-driven disease that causes platelet over-activity, the mechanism for TTS is completely different from other types of blood clot.
In this light, ATAGI recently advised the AstraZeneca vaccine is safe for these people.