Immune thrombocytopenic purpura in an elderly patient with cerebral hemorrhage after the fourth mRNA-1273 COVID-19 vaccination

"Discussion

The patient had received the mRNA-1273 COVID-19 vaccine, the same as received in three previous doses, 21 days before admission. As his platelet count before vaccination was consistently normal and no other apparent cause was found, we diagnosed acute de novo immune thrombocytopenic purpura (ITP) related to vaccination. Most reports of ITP after SARS-CoV-2 vaccination have occurred after the first or second vaccination, and this is the first report after the fourth vaccination.

Although the cause of ITP after SARS-CoV-2 vaccination remains unclear, molecular homology between viral proteins and autologous platelets and immunologic-enhancing effects of adjuvants have been reported. In the present case, it is noteworthy that the immature platelet fraction (IPF) was 0.0% and showed no increase, despite the markedly decreased platelet count at the time of admission. Some reports have been skeptical regarding a direct effect of the SARS-CoV-2 vaccine, a type of inactivated vaccine, on megakaryocytes; however, it has been pointed out that even before the COVID-19 pandemic, antigen–antibody reaction against megakaryocytes, opsonization, and induction of apoptosis were considered possible mechanisms of post-vaccination ITP. The fact that IPF showed no elevation at admission in our patient, who had petechial hemorrhage 7 days prior to admission, suggests a direct effect of the vaccine on the platelet-producing capacity of megakaryocytes. In addition, it has been suggested that early introduction of a thrombopoietin receptor agonist may lead to early recovery of platelet production in patients with low IPF."