The COVID-19 pandemic has led to unprecedented demand on the global healthcare system. Remarkably, at the end of 2021, COVID-19 vaccines received approvals for human use in several countries worldwide. Since then, a solid base for response in the fight against the virus has been placed. COVID-19 vaccines have been shown to be safe and effective drugs. Nevertheless, all kinds of vaccines may be associated with the possible appearance of neurological complications, and COVID-19 vaccines are not free from neurological side effects. Neurological complications of COVID-19 vaccination are usually mild, short-duration, and self-limiting. However, severe and unexpected post-vaccination complications are rare but possible events. They include the Guillain-Barré syndrome, facial palsy, other neuropathies, encephalitis, meningitis, myelitis, autoimmune disorders, and cerebrovascular events. The fear of severe or fatal neurological complications fed the “vaccine hesitancy” phenomenon, posing a vital communication challenge between the scientific community and public opinion. This review aims to collect and discuss the frequency, management, and outcome of reported neurological complications of COVID-19 vaccines after eighteen months of the World Health Organization’s approval of COVID-19 vaccination, providing an overview of safety and concerns related to the most potent weapon against the SARS-CoV-2.

The pathophysiology of cognitive impairment (CI) in multiple sclerosis (MS) remains unclear. Meningeal B cell aggregates may contribute to cortical grey matter pathology. Cerebrospinal fluid (CSF), kappa free light chains (KFLC), and KFLCs-Index (kappa-Index) are reliable quantitative markers of intrathecal synthesis, but few data have been presented exploring the association with CI, and no data are present for lambda FLC (LFLC) in MS. We evaluated cognition using the Brief International Cognitive Assessment for MS (BICAMS) battery and collected serum and CSF at diagnosis in newly diagnosed drug-naïve MS patients. We observed that patients with impaired verbal memory and overall CI showed increased CSF KFLCs (respectively p: 0.0003 and p: 0.003) and kappa-Index (respectively p: 0.01 and p: 0.02) compared to those with normal verbal memory and no CI. Patients with CI also displayed lower CSF LFLCs (p: 0.04) and lambda-Index (p: 0.001); however, only CSF KFLC negatively correlated with normalized results of verbal memory (for age, sex, and educational levels), even after correction for EDSS (r: −0.27 p: 0.01). Finally, CSF FKLC and kappa-Index were significant predictors of verbal memory in a multivariate analysis. Our results, suggest that intrathecal B cell activity might contribute to CI development in MS patients.