The company’s vaccine, which is manufactured by its subsidiary Janssen, has been administered to over 6.8 million people in the US. The decision by the FDA and the CDC was made after reports of six cerebral venous sinus thrombosis (CVST) blood clots, which occurred in combination with low levels of blood platelets (thrombocytopenia). All six reports occurred in women between the ages of 18 and 48, with symptoms occurring six to 13 days after vaccination.
Whereas blood clots are usually treated with an anticoagulant drug called herapin, the FDA and CDC have stated that that in this case the use of that drug may be dangerous.