The understanding that some pesticides are more hazardous than others is well established. Recognition of this is reflected by the World Health Organization (WHO) Recommended Classification of Pesticides by Hazard, which was first published in 1975. The document classifies pesticides in one of five hazard classes according to their acute toxicity. In 2002, the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) was introduced, which in addition to acute toxicity also provides classification of chemicals according to their chronic health hazards and environmental hazards.

This report from the Council for International Organizations of Medical Sciences (CIOMS) in collaboration with WHO covers the activities and outputs of the CIOMS/WHO Working Group on Vaccine Pharmacovigilance (2005-2010). This working group brought together experts from both industrialized and emerging countries representing regulatory agencies, vaccine industry, national and international public health bodies including WHO and CIOMS, academia and clinical care, contributing from their different perspectives. The report covers general terms and definitions for vaccine safety and discusses the application of such harmonized tools in vaccine safety surveillance and studies. As well, the report highlights case definitions for adverse events typically reported for vaccines. The report is addressed to those engaged in vaccine safety data collection and evaluation, and will also make a useful reading for others who want to familiarize themselves with vaccine safety terminology.