The global effort to roll out COVID vaccines suffered a blow this week when 11 European countries paused the use of the Oxford-AstraZeneca jab, after a number of people developed blood clots soon after receiving doses. Outside Europe, Indonesia also announced it would delay administering the vaccine while it awaited a review. The health authorities in these countries stated that the halting of the vaccine was merely a precautionary measure.
Four people developed blood clots a few days after having the Oxford-AstraZeneca vaccine in Norway in early March. Then, another person in Austria was admitted to a hospital with a blood clot on the lung, and he and died, 10 days after being vaccinated. Another death involving a blood clot has also been reported in Denmark.
On Thursday, after few days of investigation, however, the European Medicines Agency stated that it was satisfied the vaccine is “safe and effective” and not, after all, linked to a higher risk of developing blood clots. It will continue to conduct research. Those countries which halted the use of the vaccine can now resume.
This should put the issue to rest, but the scare has caused understandable anxiety for those who have already had their Oxford-AstraZeneca vaccine, or who may be waiting for their second dose. So, what are blood clots and what causes them?
Blood should normally flow smoothly through vessels uninterrupted. Its main job is to carry nutrition and oxygen to our organs. To maintain this smooth flow of blood, it needs to move continuously and not stand still (which is why long periods of immobility can increase your risk). It also needs the chemicals or “factors” that control blood clotting inside us to stay in balance and for the inside of our blood vessels to stay smooth so the blood doesn’t catch on anything as it flows by, which is why inflammation inside of blood vessels caused by illnesses, including COVID-19, can increase the risk of clots.
When any of these things upset the flow of blood, it can clot, forming a clump of blood that has changed from a liquid to a gel-like or semi-solid state. This clot can then travel and block a blood vessel elsewhere, such as in the lungs, causing this area to be quickly starved of food and oxygen.
Blood clots happen in about one in 1,000 people each year. These tend to be people who are older, have certain cancers, are pregnant or spend long periods not moving about.
This is the number of clots that would occur in the general population who have not had any of the COVID vaccines. According to the European Medicines Agency, as at March 10, 37 cases of thromboembolic events (blood clots) had been reported among close to five million people vaccinated with the Oxford-AstraZeneca in the European Economic Area. That is significantly fewer than what should be expected from any general population, even without being vaccinated. This number would be higher if the Oxford vaccine promoted clot formation. It is actually significantly lower.
AstraZeneca said in a statement, “A careful review of all available safety data of more than 17 million people vaccinated in the European Union (EU) has shown no evidence of an increased risk of pulmonary embolism, deep vein thrombosis (DVT) or thrombocytopenia, in any defined age group, gender, batch or in any particular country.”
On Friday, however, medical researchers in Germany said they had discovered a link between the AstraZeneca vaccine and one particularly rare type of blood clot believed to have occurred in a “very small number” of people who have received the vaccine. A cerebral venous sinus thrombosis (CVST) is a clot in part of the vessels that allow blood to drain from the brain. The symptoms of this type of blood clot include headache, blurred vision and weakness of part of the face or limbs.
The incidence of this type of blood clot is three to four people per million in the general unvaccinated population and, even with the “very small number” of people in whom this has occurred after having the vaccine, there is no related increase in cases in the vaccinated groups.
We do know that catching COVID itself can increase your risk of developing blood clots because of the inflammation it causes in the body, especially inside the blood vessels.
Many patients who are treated for coronavirus in hospital are routinely put on blood-thinning medication to reduce their risk of developing clots. As a doctor, I would say it is safer to get the Oxford vaccine than to get COVID. Mama Khan (my mum) has had her first dose of the Oxford vaccine and will be due her second one soon.
Source: Al Jazeera
