An extremely rare side effect of AstraZeneca's vaccine is thrombosis, which is different from regular thrombosis. The Medicines Agency has said people taking anti-thrombosis medicines do not need to worry about the side effects.
Blood clots that occur due to lifestyle or from certain medicines are very different in essence and frequency to the sort associated with AstraZeneca, the agency said.
While one person in 100,000 can get a blood clot associated with AstraZeneca, the risk of a normal blood clot is one in 1,000.
"There are many causes of thrombosis, ranging from lifestyle, various hormones to genetic risk factors," Toivo Maimets, professor of cell biology at the University of Tartu, told ETV's current affairs shows "Aktuaalne kaamera" on Thursday.
In the case of the AstraZeneca vaccine, there is not a normal risk of thrombosis, but the thrombus forms in another place and the composition of blood cells also changes, Maimets said.
As the blood clots that may form from AstraZeneca are different, the vaccine does not affect those who are usually at risk of blood clots.
"People at risk for normal blood clots who use the medicines for it to treat and prevent these blood clots, as well as healthy women who use contraceptives, do not have to be afraid, the vaccine does not affect the effects of these medicines in any way or increase the risk of blood clots," Maimets said.
The benefits of the vaccine outweigh the risks
Under normal circumstances, contraceptives are one of the most widely used medicines which are most likely to cause blood clots. However, a blood clot with AstraZeneca is much less likely to occur.
"If you take 10,000 women, two healthy women may have a blood clot in a year. If you start using a contraceptive, there may be five to 10 more cases per 10,000 women, depending on what's in it, so there's a higher risk of getting a blood clot than with an AstraZeneca vaccine," the Agency of Medicines head Maia Uusküla, said.
Maimets said that it must be taken into account that all medicines and vaccines have side effects. The risk-benefit balance must be considered.
"There is no doubt that all medicines have risks. If you take out any leaflet these lists are pretty long. The European Medicines Agency has always assessed, and also stated in yesterday's statement, that the risk-benefit balance is very, very strong towards the benefit side," he said.
The European Medicines Agency's statement on AstraZeneca can be read here.
Editor: Roberta Vaino