Nazmul Hossain

The coronavirus disease 2019 (COVID-19) pandemic has been associated with a wide range of neurological complications, among which persistent cognitive impairment and memory deficits are increasingly recognized as key symptoms of the post-acute sequelae of SARS-CoV-2 infection (PASC or long COVID). Although clinical and epidemiological studies have documented these symptoms across diverse patient populations, the underlying neurobiological mechanisms remain incompletely understood. Growing evidence from human studies, neuropathological analyses, and experimental models indicates that neuroimmune and inflammatory processes plays a central role in COVID-19-associated cognitive dysfunction. As the brain’s resident immune cells, microglia are vital for synaptic health, neuroplasticity, and memory, yet these processes may be compromised after SARS-CoV-2 infection. Systemic inflammation, blood–brain barrier (BBB) disruption, endothelial injury, and cytokine signaling can induce sustained microglial activation and priming, leading to inflammasome activation, complement-mediated synaptic remodeling, oxidative stress, and impaired hippocampal neurogenesis. These processes collectively disrupt neural circuits involved in learning and memory and may underlie the persistent “brain fog” reported by COVID-19 survivors. This review synthesizes clinical, biomarker, neuroimaging, and mechanistic evidence linking SARS-CoV-2 infection to microglia-mediated neuroinflammation and memory impairment. In contrast to prior reviews that broadly describe neuroinflammation in COVID-19, we integrate multidimensional evidence into a microglia-centric immunovascular framework that highlights converging pathogenic pathways underlying cognitive symptoms. We further discuss emerging biomarkers of glial activation and evaluate current and prospective therapeutic strategies targeting microglial and neuroimmune pathways. Understanding the role of microglial dysregulation in post-COVID cognitive impairment may facilitate the development of targeted interventions to mitigate long-term neurological consequences of COVID-19.

COVID-19 has raised significant concern regarding its neurological impact, particularly during the early pandemic waves when severe systemic inflammation and neuroimmune dysregulation were more common. Although SARS-CoV-2 has been extensively studied, the precise mechanisms underlying its neurological effects remain incompletely understood, and much of the available evidence is derived from early variants with higher pathogenicity. Current research indicates that neuroinflammatory processes—driven primarily by systemic cytokine elevation, microglial activation, and blood–brain barrier dysfunction—contribute to a wide range of neurological symptoms. Severe complications such as encephalopathy, stroke, and cognitive impairment were predominantly reported in critically ill patients infected with the Wuhan, Alpha, or Delta variants, while such manifestations are considerably less frequent in the Omicron era. Most proposed mechanisms, including ACE2-mediated viral entry into the central nervous system, are supported mainly by experimental or preclinical studies rather than definitive human evidence. Biomarkers such as IL-6 and TNF-α, along with neuroimaging modalities including MRI and PET, offer useful but indirect indicators of neuroinflammation. Therapeutic approaches continue to focus on controlling systemic inflammation through immunomodulatory agents, complemented by targeted non-pharmacological strategies—such as physical rehabilitation, cognitive support, and psychological interventions—for the minority of patients with persistent neurological deficits. Overall, current evidence supports a variant-dependent neuroinflammatory profile and underscores the need for longitudinal, mechanism-focused studies to better characterize long-term neurological outcomes and refine therapeutic strategies.