From the Journals

AHA guidance on blood clots linked to COVID-19 vaccine


A newly released report is offering guidance concerning rare conditions associated with COVID-19 as well as vaccines against the virus.

The report was released April 29, 2021, by the American Heart Association/American Stroke Association Stroke Council Leadership in answer to the decision April 23 by the Centers for Disease Control and Prevention and the Food and Drug Administration to lift an earlier “pause” in administration of the Johnson & Johnson (Janssen) vaccine.

That pause had been put in place after reports were received of a possible association between the J&J vaccine and cerebral venous sinus thrombosis (CVST) and thrombosis-thrombocytopenia syndrome (TTS, blood clots plus low blood platelets). CVST and TTS were also linked to patients in Europe and Canada who received the AstraZeneca COVID-19 vaccine.

However, the new report noted that these conditions are very rare.

“The risk of CVST due to infection with COVID-19 is 8-10 times higher than the risk of CVST after receiving a COVID-19 vaccine,” lead author Karen L. Furie, MD, chair of the department of neurology at Brown University, Providence, R.I., said in a press release.

“The public can be reassured by the CDC’s and FDA’s investigation and these statistics – the likelihood of developing CVST after a COVID-19 vaccine is extremely low,” said Dr. Furie, adding that the authors “urge all adults to receive any of the approved COVID-19 vaccines.”

The new guidance, which was published online April 29, 2021, in Stroke, discusses signs and symptoms of CVST and TTS, as well as vaccine-induced immune thrombotic thrombocytopenia (VITT). It also recommends best options for treating these conditions.

Assessing 81 million patients

In their analysis, the investigators assessed a database of 59 health care organizations and 81 million patients, 98% of whom were in the United States.

Of almost 514,000 patients diagnosed with COVID-19 between January 2020 and March 2021, 20 also received a diagnosis of CVST.

Among about 490,000 adults who received either the Pfizer or Moderna vaccines, there were no diagnosed cases of thrombocytopenia.

Dr. Furie reiterated that CVST blood clots “are very rare adverse events,” but recommended that any patient in the ED with a suspected clot should be screened immediately to determine if they received a COVID vaccine during the previous few weeks.

For those who have recently received the COVID-19 vaccine, a suspected clot should be treated with nonheparin anticoagulants, Dr. Furie said.

“No heparin products in any dose should be given for suspected CVST, TTS, or VITT. With the right treatment, most patients can have a full recovery,” she added. The report includes additional, detailed treatment recommendations if one of these conditions are suspected.

Rare events

The authors noted that cases of TTS/VITT occurred up to 2.5 weeks after receiving the J&J vaccine in the United States and up to 3.5 weeks after receiving the AstraZeneca vaccine in Europe.

An April 23 report from the CDC and FDA noted that, out of almost 7 million adults who received the J&J vaccine, the agencies investigated only 15 reported cases of TTS.

An April 7 report from the European Medicines Agency noted that, out of more than 25 million people who received the AstraZeneca vaccine in the European Union, it found 62 cases of CVST.

A statement put out by the American Heart Association/American Stroke Association urges “everyone to receive a COVID-19 vaccine” as soon as possible.

“We are confident the benefits of vaccination far exceed the very small, rare risks,” the organizations said. “The risks of vaccination are also far smaller than the risk of COVID-19 and its potentially fatal consequences.”

A version of this article first appeared on

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