Evidence suggests that an unusual immune response is the cause of 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 the millions of people vaccinated with AstraZeneca’s or Johnson & Johnson’s COVID-19 injections have developed serious blood clots, such as those in the sinuses that drain blood from the brain (SN: 7-4-21; 13/04/21A few have passed away.
Studies suggest that some inoculated people develop an immune response that attacks the protein platelet factor 4 or PF4, causing platelets to form clots. Those platelets run out before the body can produce more. So these patients end up with both the rare clots and low platelets.
Of the 23 patients who received the AstraZeneca shot and had symptoms of clots or low platelets, 21 tested positive for antibodies to PF4, researchers report April 16 in the report. New England Journal of MedicineOf these, 20 people developed blood clots. The finding adds to previous studies that found the same antibodies in other patients who received the injection of AstraZeneca and had the dangerous clots.
Five of the six women who had blood clots after receiving an injection from Johnson & Johnson in the United States also had PF4 antibodies, health officials said April 14 at a meeting of the Advisory Committee on Immunization Practices. That advisory group from the U.S. Centers for Disease Control and Prevention is assessing what needs to be done to overcome a temporary pause in administering the Johnson & Johnson shot prompted by concerns about blood clots (SN: 13-4-21One man had developed brain sinus clots during the clinical trial of the injection and a seventh case is under investigation, the pharmaceutical company said at the meeting.
“Because we are aware of this syndrome … we know how to treat it,” said Jean Connors, a clinical haematologist 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 clots before officials established the link, “we can diagnose it faster and treat it better if it does happen, so the results will be better.”
That’s 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 binds 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 develop more blood clots, Connors says. For example, four out of 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 a woman was released from the hospital. Three of them were still hospitalized as of April 14.
Health professionals 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, not-for-profit news organization.
Stay up to date with the news and opinions of San Antonio. Sign up for our Weekly Newsletter.