Thromboembolic Events in the South African Ad26.COV2.S Vaccine Study

This correspondence presents interim safety data from the Sisonke phase 3b implementation trial of the single-dose Ad26.COV2.S Covid-19 vaccine administered to healthcare workers in South Africa. Of 288,368 vaccinated participants, 2% reported adverse events, with 50 meeting criteria for serious or special interest. These included allergic reactions, neurologic events (e.g., Guillain-Barré syndrome, Bell's palsy), and thromboembolic events. Five thrombotic/embolic cases—such as pulmonary embolism, cerebrovascular infarcts, and retinal vein occlusion—occurred in individuals with predisposing risk factors. No case of vaccine-induced immune thrombotic thrombocytopenia (VITT) was documented. The report concludes that the overall rate of adverse events was low and events were primarily attributable to underlying conditions rather than vaccine causality

This correspondence presents interim safety data from the Sisonke phase 3b implementation trial of the single-dose Ad26.COV2.S Covid-19 vaccine administered to healthcare workers in South Africa. Of 288,368 vaccinated participants, 2% reported adverse events, with 50 meeting criteria for serious or special interest. These included allergic reactions, neurologic events (e.g., Guillain-Barré syndrome, Bell's palsy), and thromboembolic events. Five thrombotic/embolic cases—such as pulmonary embolism, cerebrovascular infarcts, and retinal vein occlusion—occurred in individuals with predisposing risk factors. No case of vaccine-induced immune thrombotic thrombocytopenia (VITT) was documented. The report concludes that the overall rate of adverse events was low and events were primarily attributable to underlying conditions rather than vaccine causality