Whilst most of the patients in this data set were young and female, not all are.
Among the 23 patients included in this study, the median age was 46 years (range, 21 to 77), with 16 patients (70%) younger than 50 years. Fourteen patients (61%) were female. All the patients were reported as previously fit and well by referring hospitals, with no history of a medical condition or use of a medication likely to precipitate thrombosis, except for 1 patient who had a history of deep venous thrombosis and 1 patient who was known to be taking the combined oral contraceptive pill. All the patients had received the first dose of the ChAdOx1 nCoV-19 vaccine 6 to 24 days (median, 12 days) before presentation. Mild bruising and petechiae were evident in some patients. Secondary cerebral hemorrhage was noted in some patients who had cerebral venous thrombosis. The 1 patient who did not present with thrombosis had clinically significant bruising but no other hemorrhagic manifestations.
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In all cases reported to date, this syndrome of thrombocytopenia and venous thrombosis appears to be triggered by receipt of the first dose of the ChAdOx1 nCoV-19 vaccine. Although there have been a few reports of patients with symptoms consistent with this clinical syndrome after the receipt of other vaccines against SARS-CoV-2, none have yet been confirmed to fulfill the diagnostic criteria, specifically the presence of thrombocytopenia, thrombosis, a very high d-dimer level, and a low or normal fibrinogen level. Furthermore, in Israel, where two doses of the BNT162b2 vaccine (Pfizer–BioNTech) have been provided to more than 4 million people, no cases of this rare syndrome have been reported. Although natural SARS-CoV-2 infection has been associated with thromboembolic phenomena, those events differ from the specific syndrome described in this study.
The risk of Covid-19 remains a serious public health consideration worldwide, and vaccination against SARS-CoV-2 provides critical protection.24 There is a substantial risk of ascertainment bias when associating adverse clinical events with vaccination; however, the syndrome described in this study has a combination of clinical and laboratory features that is exceptional and has not been previously observed by any of the authors who are specialist hematologists or neurologists. Ongoing data collection and studies could help to establish whether and how the development of pathologic platelet-activating anti-PF4 antibodies, unrelated to the use of heparin therapy, could be associated with vaccination against SARS-CoV-2.
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In all cases reported to date, this syndrome of thrombocytopenia and venous thrombosis appears to be triggered by receipt of the first dose of the ChAdOx1 nCoV-19 vaccine. Although there have been a few reports of patients with symptoms consistent with this clinical syndrome after the receipt of other vaccines against SARS-CoV-2, none have yet been confirmed to fulfill the diagnostic criteria, specifically the presence of thrombocytopenia, thrombosis, a very high d-dimer level, and a low or normal fibrinogen level. Furthermore, in Israel, where two doses of the BNT162b2 vaccine (Pfizer–BioNTech) have been provided to more than 4 million people, no cases of this rare syndrome have been reported. Although natural SARS-CoV-2 infection has been associated with thromboembolic phenomena, those events differ from the specific syndrome described in this study.
The risk of Covid-19 remains a serious public health consideration worldwide, and vaccination against SARS-CoV-2 provides critical protection.24 There is a substantial risk of ascertainment bias when associating adverse clinical events with vaccination; however, the syndrome described in this study has a combination of clinical and laboratory features that is exceptional and has not been previously observed by any of the authors who are specialist hematologists or neurologists. Ongoing data collection and studies could help to establish whether and how the development of pathologic platelet-activating anti-PF4 antibodies, unrelated to the use of heparin therapy, could be associated with vaccination against SARS-CoV-2.
