Rare blood clots more likely after COVID-19 infection than from vaccine, report finds

An analysis led by Brown University neurologist Dr. Karen L. Furie in partnership with the American Heart Association/American Stroke Association, put the post-vaccine risk of CVST in perspective.

PROVIDENCE, R.I. [Brown University] — The rare blood clot disorder reported by some Johnson & Johnson coronavirus vaccine recipients is also a risk of COVID-19 infection, according to a new report by the American Heart Association/American Stroke Association Stroke Council Leadership.

Dr. Karen L. Furie, chair of the Department of Neurology at Brown’s Warren Alpert Medical School, served as lead author of the report, which synthesized existing data from more than 81 million patients and found that risk of developing CVST blood clots is eight to 10 times higher following a COVID-19 infection as compared to the risk associated with receipt of a COVID-19 vaccine.

While national news coverage has focused on reports of the CVST blood clot/stroke condition — cerebral venous sinus thrombosis — following vaccination, the report, published in the journal Stroke, puts the risk in perspective.

“COVID-19 infection is a significant risk factor for CVST…” Furie said. “The likelihood of developing CVST after a COVID-19 vaccine is extremely low. We urge all adults to receive any of the approved COVID-19 vaccines.”

Furie added that the public should be reassured by investigations by the U.S. Centers for Disease Control and Prevention and U.S. Food & Drug Administration into the connection, as well as by the data in the report.

The CDC and FDA had called for a temporary pause in the administration of Johnson & Johnson’s COVID-19 vaccine after reports of CVST, which is characterized by blood clots in the brain’s veins (not in the arteries, as is the case for most strokes) in combination with thrombocytopenia (low blood platelet count). The two together are called thrombosis-thrombocytopenia syndrome, or TTS. When TTS is linked to receiving a COVID-19 vaccine, it is called vaccine-induced immune thrombotic thrombocytopenia, or VITT. CVST has also been associated with cases of TTS in adults who received the AstraZeneca COVID-19 vaccine available in Europe, according to the European Medicines Agency.

After reports about CVST following vaccination emerged in April, the American Heart Association/American Stroke Association Stroke Council Leadership convened quickly to provide guidance about the signs and symptoms of CVST and related conditions, as well as about the best treatment options. Their goal was to heighten awareness of the apparent association between COVID-19 vaccinations and CVST (plus low platelets) and suggest approaches to management.

The report led by Furie included data from 59 health care organizations, totaling 81 million patients, more than 98% of whom were in the U.S. Among the nearly 514,000 patients in the database who were diagnosed with COVID-19 infection from Jan. 20 through March 25, 2021, 20 were diagnosed with CVST. The researchers compared that rate to the incidence of CVST in adults who received either the Pfizer or Moderna COVID-19 vaccine before March 25, excluding those who had previously been diagnosed with COVID-19. No cases of thrombocytopenia (low platelets) were diagnosed among almost 490,000 vaccinated adults.

The report also detailed treatment for suspected CVST, TTS or VITT. Although CVST blood clots are very rare adverse events, Furie said that all patients who arrive in the ER with a suspected clot should be immediately screened and asked whether they’d received a COVID-19 vaccination during recent weeks. The report also notes that patients who present with the symptoms of CVST or blood clots and who have low platelet counts and an antibody to platelet factor 4 should be treated using non-heparin anticoagulants.

“With the right treatment,” Furie said, “most patients can have a full recovery after CVST, TTS or VITT.”

She added that physicians and researchers are learning about the intricacies of COVID-19 live, in real-time with the patients they see in hospitals every day.

“Further research and investigation are necessary as the pandemic continues,” Furie said. “We will need data and robust research on the people who did not develop blood clots after the vaccine, too, so that we can fully understand the molecular and cellular mechanisms underlying CVST related to COVID-19 infection or after vaccination.”