It is being shown that there is an uncommon immune response behind dangerous but incredibly rare blood clots, associated with some COVID-19 vaccines. But the good news is that there is evidence that doctors can use to identify it and get patients the right care.
A small number of the millions of people vaccinated with COVID-19 shots from AstraZeneca or Johnson & Johnson have developed severe blood clots, such as sinuses that drain blood from the brain (SN: 7/04/21; 13/04/21). Some have died.
Studies suggest that some inoculated people develop an immune response that attacks a protein called platelet factor 4 or PF4, which causes platelets to form clots. These platelets run out before the body can do more. Therefore, these patients end up with rare clots and low blood platelet levels.
Of the 23 patients who received the AstraZeneca puncture and had symptoms of clots or low platelets, 21 tested positive for PF4 antibodies, the researchers reported on April 16. New England Journal of Medicine. Of these, 20 people developed blood clots. The finding adds to previous studies that found the same antibodies in additional patients who received the AstraZeneca shot and had dangerous clots.
Five out of six women who had clots after receiving Johnson & Johnson’s shot in the United States also had PF4 antibodies, health officials reported on April 14 during a meeting of the Advisory Committee on Immunization Practices. This advisory group from the U.S. Centers for Disease Control and Prevention is evaluating what needs to be done to lift a temporary pause in Johnson & Johnson jab administration caused by blood clot problems (SN: 13/04/21). A man had developed cerebral sinus clots during the clinical trial of the shooting and a seventh case is being investigated, the pharmaceutical company said during the meeting.
“Because we’re aware of this syndrome … we know how to treat it,” says Jean Connors, a clinical hematologist at Harvard Medical School and Brigham and Women’s Hospital in Boston who didn’t participate in the studies. And, unlike people who developed clots before officials identified the link, “we can diagnose it more quickly and treat it more appropriately if it occurs, so the results will be better.”
This is because vaccine-induced clots are similar to a condition called heparin-induced thrombocytopenia or HIT. Patients with HIT develop blood clots when treated with heparin, a commonly used anticoagulant drug. Heparin binds to the PF4 protein and some people develop an immune response that attacks both molecules.
Treating vaccinated patients who have PF4 antibodies with heparin is like “adding fuel to the fire” and can cause them to develop more clots, Connors says. Four of the six U.S. women who developed clots after receiving the Johnson & Johnson vaccine, for example, received heparin, as did the man in the clinical trial. The man recovered and a woman was discharged from the hospital. Three were still hospitalized as of April 14th.
Healthcare workers can take PF4 tests. And if a patient tests positive, there are many other anticoagulants other than heparin that doctors can use for treatment, Connors says.
That story was originally published by Science News, an independent non-profit news organization.
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