All 6 cases occurred in women 18-48 years old. Symptom onset occurred 6-13 days after administration of the single-dose vaccine. In addition to CVST, three of the women had extracranial thromboses. Four women developed intraparenchymal brain hemorrhage, and one died. Comorbid conditions included obesity (n=3), hypertension (n=1), hypothyroidism (n=1), and asthma (n=1); one woman was taking estrogen/progesterone.1-3

CVST with thrombocytopenia has also been reported with the Oxford/AstraZeneca adenovirus-based COVID-19 vaccine (not authorized for use in the US). With both adenovirus-based vaccines, incidence of CVST with thrombocytopenia has been associated with high serum levels of antibodies against platelet factor 4 (PF4)-polyanion complexes similar to those that occur in heparin-induced thrombocytopenia (HIT). No cases of CVST with thrombocytopenia have been associated with the ~180 million Pfizer and Moderna mRNA-based COVID-19 vaccine doses administered in the US.3-5

The CDC recommends that persons who experience a thrombotic event and thrombocytopenia after administration of the Johnson & Johnson vaccine be screened with a PF4 HIT enzyme-linked immunosorbent assay (ELISA) and referred to a hematologist. If the assay is positive or cannot be completed, heparin should not be used for thrombosis management; other anticoagulants and intravenous immune globulin should be considered instead.2