Field evaluation of vaccine safety.

Surveillance of adverse events in the field represents an essential part of vaccination strategies. Safety studies conducted before vaccine licensure have often not enough power to detect rare or long-term adverse events. Furthermore, adverse events may be caused by incorrect procedures of storage or administration. Conducting surveillance of adverse events in the field is necessary for detecting unexpected increases in incidence of adverse events, for continuing education of health personnel involved in vaccine programs, for providing appropriate information to the public, and for supporting interventions to prevent further adverse events. Signals generated by surveillance systems may stimulate to conduct formal studies to assess causality.