BACKGROUND Analysis of spontaneous reports of Adverse Events Following Immunization (AEFIs) is an important way to identify potential problems in vaccine safety and efficacy and summarize experience for dissemination to health care authorities. However, current reporting methods are not sufficiently controlled. While there is general adoption of Medical Dictionary of Regulatory Activities (MedDRA) in the reporting systems we consider, definitions are not provided for MedDRA terms, reports are

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... t annotated in a consistent manner, differing in experience of annotator, and annotation is done either at entry time, or post-hoc. Sometimes, only the final adverse event code is saved, discarding evidence supporting the diagnosis. Because of these practices, interpretation of such spontaneous reports is tedious, costly and time consuming. The Adverse Event Reporting Ontology (AERO) we are building plays a role in increasing accuracy and quality of reporting, ultimately enhancing response time to adverse event signals.