Ttwo vaccines: the Johnson & Johnson vaccine in the U.S. and the AstraZeneca vaccine in Europe, have been linked to an increased likelihood of a rare type of blood clot. Researchers are investigating what causes these clots and are beginning to propose some answers. Dr. Mousumi Som, a professor of medicine at Oklahoma State University, explains what these rare clots are and how they are formed after people get vaccinated.
1. What are blood clots?
There are a small number of people in the US developed dangerous blood clots after receiving the Johnson & Johnson vaccine. Clots have occurred mostly in people’s brains and, paradoxically, yes associated with a low platelet count.
Platelets usually help a person stop bleeding when injured. If it is cut or injured, the body responds by sending platelets that act as a temporary patch. The patch attracts other platelets and sticks to stop blood loss. Because platelets typically help the clotting process, this combination of low platelets and extreme clotting makes these clots medically unusual.
These specific types of clots, called cerebral venous sinus thrombosis, although rare, affect around from two to five people per million a year and they are potentially life-threatening without treatment. Vaccines do not usually trigger this type of clot.
2. Who has these clots?
On April 24, 2021, of the eight million people vaccinated with the Johnson & Johnson vaccine in the U.S., approximately 16 people have developed these blood clots. Clots occurred six to 13 days after vaccination, and most were present women between 18 and 48 years old.
On April 26, 2021, the news indicated that at least a man had developed a clot. The man is in his thirties and was hospitalized for a clot in his leg about two weeks after receiving the Johnson & Johnson vaccine.
European health officials have also reported that the AstraZeneca vaccine, a COVID-19 vaccine authorized and approved in Europe but not in the US, has caused 200 cases of low platelet coagulation. It is important to note that both the Johnson & Johnson vaccine and the AstraZeneca vaccine use a type of harmless virus called adenovirus to deliver instructions to the human body on how to build an immune response to COVID-19. This is called a viral virus vaccine.
The fact that both vaccines use a viral vector and that both are associated with blood clots has made many health experts think than the clotting problems of the two vaccines can share the same mechanism.
3. Why do women have more clots than men?
At this point, doctors still don’t know what makes them women more susceptible than men, nor what puts a person at risk for these clots. These clots can occur, although rarely, in people who do not receive a vaccine. Scientists know that women are three times more likely to develop this type of clot without receiving the vaccine. Many researchers think this is due to this birth control or other hormonal substitutions which women take.
4. Why can vaccines cause blood clots?
Researchers believe this is specific low platelet coagulation it is similar to a reaction that some individuals have when they do receive an anticoagulant called heparin, called heparin-induced thrombocytopenia.
Doctors sometimes use heparin to thin a person’s blood in the event of a heart attack or blood clot when blood flow needs to be restored. But some people experience the opposite reaction and their blood ends up clotting more. This is because the body triggers an unwanted immune response after receiving heparin.
In these patients, heparin binds to a product released from platelets called platelet factor 4. When this happens, the immune system considers combined platelet factor 4 and heparin a problem, so it creates antibodies in response. . These antibodies bind to the factor 4 complex of heparin and platelets and the body, which now believes it needs to repair an injury, causes more clotting while using even more platelets. That it results in a low platelet count observed in these patients.
When doctors analyzed the blood of patients who developed clots after receiving the Johnson & Johnson or AstraZeneca vaccine, it looked very similar to the blood of people who had a low platelet clotting reaction to heparin. This has led scientists and doctors to believe that the the same process could be causing these clots caused by both vaccines.