Post-COVID cognitive impairment is common after SARS-CoV-2 infection regardless of acute disease severity. Mechanisms are poorly understood, limiting our ability to prevent cognitive decline for a growing number of veterans. Identifying markers of risk for cognitive decline in post-COVID-19 syndrome is crucial for effective prevention and treatment strategies. Silent brain infarctions (SBIs), covert cerebrovascular events associated with risk of cognitive impairment, are prevalent in COVID-19 survivors. Although mechanisms are unclear, it is plausible that they are ischemic manifestations of platelet hyperreactivity in COVID-19. Coated- platelets, a strongly procoagulant subset of platelets produced after co-activation with collagen and thrombin, are associated with ischemic stroke risk and the presence and number of SBIs on brain imaging from patients with vascular risk factors. Preliminary work from VA funded research in veterans with COVID-19 showed that increased coated-platelet levels predicted death at 90 days. In survivors, SARS-CoV-2 infection significantly altered platelet procoagulant potential, with a sharp and sustained increase in coated-platelet levels noted during convalescence. RNA sequencing in platelets obtained during acute infection identified an association between pannexins and coated-platelet levels. In the same cohort, 39.4% reported brain fog symptoms a year after infection, and 58.6% screened positive for cognitive impairment on the Montreal Cognitive Assessment (MoCA) at 14 months. Importantly, mean coated-platelet levels measured during acute infection were significantly inversely associated with future MoCA score. Lastly, in a separate cohort of veterans with mild cognitive impairment, SARS-CoV-2 infection and age were significant predictors of progression to dementia at 18 months. Comparison of brain imaging before and after SARS-CoV-2 infection showed accumulation of new SBIs following infection in those who progressed. Our central hypothesis, supported by our preliminary findings, is that cognitive dysfunction in veterans with post-COVID-19 syndrome is mediated by accumulation of SBIs, which is accelerated among those whose coated-platelet levels are elevated during and after SARS- CoV-2 infection. Our long-range objective is to develop strategies for preventing cognitive decline after recovery from COVID-19. The objective of the current application is to determine the role of coated-platelets as predictors of cognitive dysfunction and SBI after recovery from COVID-19. Three specific aims will test our hypotheses. Aim 1 will confirm and extend our preliminary findings showing an association between coated- platelet levels and cognitive dysfunction after recovery from COVID-19. Coated-platelet levels will be assayed in veterans with a history of SARS-CoV-2 infection, and the association between 1) cognitive impairment on formal neuropsychological testing and 2) the presence of SBI on MRI determined. Aim 2 will chara...