Evidence shows that an unusual immune response is behind dangerous, but incredibly rare, blood clots associated with some COVID-19 vaccines. But the good news is that there is a test that doctors can use to identify it and give patients the right care.
A small number of people out of the millions vaccinated with Johnson & Johnson’s AstraZeneca or COVID-19 shots developed severe blood clots, such as in the sinuses that draw blood from the brain (SN: 7/7/21; 13/4/21). Some died.
Studies suggest that some vaccinated people develop an immune response that attacks a protein called platelet factor 4 or PF4, which forms platelets. Those platelets run out before the body can make any more. These patients therefore end up with the rare blood clots and low levels of platelets.
Of 23 patients who received AstraZeneca’s jab and had symptoms of blood clots or low platelets, 21 tested positive for antibodies to PF4, researchers reported on April 16. New England Journal of Medicine. Of these, 20 people received blood clots. The finding contributes to previous studies that found the same antibodies in additional patients who received AstraZeneca’s shot and had the dangerous blood clots.
Five of six women who had blood clots after receiving the shot from Johnson & Johnson in the United States also had PF4 antibodies, health officials said on April 14 during a meeting of an advisory committee on immunization practices. The Advisory Group for the U.S. Centers for Disease Control and Prevention considers what needs to be done to provide a temporary break in the administration of the Johnson & Johnson jab caused by blood clot disorders (SN: 13/4/21). One man developed the sinus clots of the brain during the clinical examination and a seventh case is being investigated, the pharmaceutical company said during the meeting.
“Because we are aware of this syndrome … we know how to treat it,” said Jean Connors, a clinical hematologist at Harvard Medical School and Brigham and Women’s Hospital in Boston, who was not involved in the studies. . And unlike the people who developed the blood clots before officials fixed the link, ‘we can diagnose it faster and treat it better appropriately if it happens, so the outcomes will be better.’
This is because the vaccine-induced clots are similar to a condition called heparin-induced thrombocytopenia, or HIT. Patients with HIT develop blood clots when treated with the commonly used anticoagulant heparin. Heparin attaches to the PF4 protein, and some people develop an immune response that attacks the two molecules.
Treating vaccinated patients who have PF4 antibodies with heparin is like adding fuel to the fire and can cause them to get more blood clots, Connors says. For example, four of the six American women who developed blood clots after receiving the Johnson & Johnson vaccine received heparin, just like the man in the clinical trial. The man recovered and one woman was discharged from the hospital. Three were still admitted to hospital from April 14.
Healthcare workers can test for PF4. And if a patient tests positive, there are many other anticoagulants besides heparin that clinicians can use for treatment, Connors says.
This story was originally published by Science News, an independent, non-profit news organization.
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