Understanding risk of thrombosis with thrombocytopenia syndrome after Ad26.COV2.S vaccination

On April 13,2021,the US Centers for Disease Control and Prevention(CDC)and the US Food and Drug Adminis-tration(FDA)recommended a pause in administration of the Ad26.COV2.S(Johnson&Johnson[Janssen])cor-onavirus disease 2019(COVID-19)vaccine for all persons[1].At that time,approximately 6.8 million doses of vaccine had been administered around the United States.