This document includes a Brighton Collaboration case definition of the term “Sensorineural Hearing Loss” (SNHL) as well as guidelines for data collection, analysis, and presentation of immunization safety data. This resource is to be utilized in the evaluation of adverse events following immunization. The case definition was developed by a group of experts convened by the Coalition for Epidemic Preparedness Innovations (CEPI) as part of the Safety Platform for Emergency vACcines (SPEAC) project, in the context of active development of vaccines for Lassa fever and other emerging pathogens. The case definition format of the Brighton Collaboration was followed to develop a consensus case definition and defined levels of diagnostic certainty, after an exhaustive review of the literature and expert consultation.