Among the various events reported as adverse outcomes following immunizations, neurologic adverse events following immunization (AEFI) are among the most severe and the most difficult to assess. The multifaceted presentation of neurologic illness, the relative lack of familiarity of many clinicians with the approach to and diagnosis of neurologic disease, and the relative scarcity of trained neurologists in many parts of the world make neurologic AEFI some of the most challenging issues in clinical vaccinology. Further, the severity of central and peripheral nervous system events in individual patients often heightens the concern when such illnesses are associated with antecedent immunizations. The lack of a common definition of GBS and FS hinders comparability and uniform reporting of these adverse events.

Sections 2 and 3 of this paper provide the case definitions and guidelines for data collection, analysis, and presentation that the Brighton Collaboration GBS Working Group (hereafter referred to as the Working Group) has developed for the standardized collection and assessment of information about GBS and FS. Widespread use of these definitions with their guidelines will improve data comparability and allow for a better understanding of these neurological events that are applicable in study settings with different availability of resources, in health care settings that differ by availability of and access to health care, and in different geographic regions.