From the American Heart Association Statement on "CVST and blood clots potentially related to the J&J COVID-19 vaccine: know the symptoms":

April 15, 2021 – Earlier this week, the Centers for Disease Control and Prevention (CDC) and the U.S. Food & Drug Administration (FDA) recommended a pause in administration of the Johnson & Johnson (Janssen) COVID-19 vaccine because six women, ages 18-48 years, of the nearly 7 million adults who have received this vaccine experienced cerebral venous sinus thrombosis (CVST), or blood clots in the brain’s veins (not in the arteries, as is the case for most strokes).

CVST is an extremely rare but serious type of stroke caused by a blood clot in a part of the brain known as the venous sinus, involving veins that carry blood away from the brain. Spontaneous CVST is estimated to affect 5 of every 1 million people in the world annually. It can cause serious disability or even death. In contrast, the vast majority of strokes (approximately 87% of nearly 800,000 strokes in the U.S. annually) are ischemic strokes – blood clots in the arteries that lead to interruption of nourishing blood flow to the brain.

The full AHA Statement is available online at the AHA Newsroom.

This collection pulls together some of the latest research on cerebral venous and cerebral venous sinus thrombosis published in the AHA/ASA journal Stroke.

The full collection of AHA/ASA Journal articles related to the COVID-19 pandemic is available here and additional resources can be found at the AHA's Professional Heart Daily.