A rare and dishonest immune response is the main suspect, as authorities are investigating extremely unusual blood clots following the use of two similar COVID-19 vaccines from Johnson & Johnson and AstraZeneca.
The US recommended that states discontinued the J&J vaccine on Tuesday, as authorities examined six reports of unusual clots, including one death, from more than 6.8 million Americans who have been given the single-dose vaccine so far.
The small number of cases has caused concern, as just last week, European authorities said similar clots could be linked to the AstraZeneca vaccine, which is not yet OK in the US, which has led some countries to limit its use to certain groups. of age.
Also on Tuesday, J&J delayed its imminent European launch.
What makes these different clots?
These are not typical blood clots. They’re weird in two ways.
First, they occur in unusual parts of the body, such as veins that drain blood from the brain. Second, those patients also have abnormally low levels of platelets – cells that help clots – a condition normally associated with bleeding, not clotting.
Scientists in Norway and Germany have first raised the possibility that some people may experience an abnormal immune system response to the AstraZeneca vaccine, forming antibodies that attack their own platelets. That’s the theory, as the United States is now investigating clots in patients with the J&J vaccine, Dr. Peter Marks, head of the Food and Drug Administration’s vaccine, said Tuesday.
WHY SUSPECTED IMMUNE RESPONSE?
The first clue: a widely used blood thinner, called heparin, sometimes causes a very similar side effect. Very rarely, heparin recipients form antibodies that attack and overstimulate platelets, said Dr. Geoffrey Barnes, a clot expert at the University of Michigan.
“It can cause both sides of the blood clotting spectrum,” Barnes said.
Because heparin is used so often in hospitals, this reaction is something “that every hospital in America knows how to diagnose and treat.”
There are also incredibly rare reports of this strange combination of clot-platelets in people who have never taken heparin, such as after an infection. Those unexplained cases did not receive much attention, Barnes said, until the first reports of clots appeared in some beneficiaries of the AstraZeneca vaccine.
Health officials said one reason for the J&J break was to make sure doctors knew how to treat patients suspected of having these clots, which includes avoiding heparin.
The Centers for Disease Control and Prevention later on Tuesday offered advice on how to detect and treat unusual clots.
WHAT DOES THE RESEARCH DISPLAY?
In two studies in the New England Journal of Medicine last week, research teams in Norway and Germany found antibodies that attack platelets in the blood of AstraZeneca vaccine recipients who had strange clots. The antibodies were similar to those found with the side effect of heparin, even though the patients never used that blood thinner.
It is not yet clear if there is a similar link to the J&J vaccine. But the J&J and AstraZeneca vaccines, as well as a Russian COVID-19 vaccine and one from China, are made with the same technology. They train the immune system to recognize the spike protein that covers the coronavirus. To do this, they use a cold virus, called an adenovirus, to carry the spike gene into the body.
The FDA would not say whether strange clots may be common to these so-called adenovirus-vector vaccines. In addition to AstraZeneca data, J&J makes an Ebola vaccine in the same way and said authorities will examine “all the evidence.”
WHAT ABOUT OTHER VACCINES?
The most widely used COVID-19 vaccines in the United States – from Pfizer and Moderna – are made with a completely different technology, and the FDA said there is no sign of a similar concern about clots with these vaccines.
But people worried about getting the J&J vaccination? Marks said it’s important not to confuse the risk of rare clots with normal flu-like symptoms that people often feel a day or two after vaccinating COVID-19. He said that in terms of symptoms, such as severe headaches or severe abdominal pain, they will appear one to three weeks after the J&J vaccine.
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