![]() A small number of cases have been reported in older adults. However, it is not yet certain age is a risk factor. It’s unusual because in all the other cases of this kind of thrombosis it’s the older population that’s at higher risk.” So in the case of the vaccine, it seems more likely younger people will have an overactive immune system. “In one cohort studied of people who had this reaction after the vaccine, everyone affected, except one person, was under 50,” Perdomo said. With the vaccine-induced syndrome, it appears people aged under 50 are more likely to be affected. Usually, the older you are, the more susceptible you are to heparin-induced thrombocytopenia, Perdomo said. Perdomo said there are some differences between the heparin-induced and vaccine-induced clotting conditions, and age seems to be one of them. What other theories are being investigated?Ī report from the European Medicines Agency (EMA) stated that all possible options should be taken into consideration, such as possible quality defects or impurities in vaccine batches or matter introduced during the administering of the vaccine. And that complex is what activates platelets and other blood cells to form clots,” Perdoma said. That is, antibodies are being produced against platelet factor 4. “What we know is the final complex is the same. That inflammation will lead to the production of cell-free DNA, and then the formation of the immune complex that leads to clotting. The other theory is that there may be some people predisposed to developing inflammation from the vaccine. “But that is just speculation and hasn’t been shown to be the case yet.” “So that DNA in some people can get into the circulation and trigger these same complexes,” he said. Perdoma said one theory as to why the vaccine is triggering that antibody response against platelet factor 4 is that the AstraZeneca vaccine has DNA in it. Once that complex is there, you have all these reactions including the activation of clotting for example.” “That complex is the one that gives rise to antibodies which see this complex as an invading bacteria. ![]() “That DNA somehow behaves like heparin – that the molecule, in this case DNA, can form complexes with the protein called platelet factor 4,” Perdomo said. That’s because infections can lead the body to produce what is called cell-free DNA, which is basically extracellular DNA from dying cells in the blood (though cell-free DNA can also derive from normal cells). “One is that some people are already predisposed to this condition because of previous bacterial or viral infections,” Perdomo said. ![]() The exact mechanism causing the vaccine-induced thrombosis with thrombocytopenia may never be known, he said. He said much is still unknown about why heparin-induced thrombocytopenia occurs, and that condition was first reported in the 60s. What’s causing this clotting?ĭr Jose Perdomo, a senior research officer in the haematology research unit at the University of New South Wales St George and Sutherland clinical school, said: “We know what’s happening, but the ‘why’ is not known.” Those affected by the syndrome after receiving the AstraZeneca vaccine also have the same complex, with antibodies to platelet factor 4 in their plasma. In those affected after being given heparin, the immune system makes antibodies to a complex of heparin and a protein called “platelet factor 4”, triggering this dangerous clotting. In both heparin use and administration of the AstraZeneca vaccine, the rare clotting disorder appears within two weeks, usually between day four and 20. ![]() The condition is very similar to another relatively rare but serious clotting condition caused by the use of a blood thinner called heparin. ![]()
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