Causes of adverse events following immunization

In December 2010, in view of the difficulties many countries have had in evaluating individual cases or clusters of AEFIs, GACVS convened a group of experts to review the WHO guidelines on assessing the causes of serious AEFIs. The guidelines are intended to be used for assessment of individual cases of serious AEFIs in order to evaluate whether they are related to vaccination. The review is in progress. Its aim is to develop a simple, objective, transparent and evidence-based approach to help national and regional authorities determine whether a serious AEFI reported through pharmacovigilance is likely to have been caused by a specific vaccine.

The new method for assessing AEFIs will be based on previous experience with specific vaccines. However, it is clear that the evaluation of serious AEFIs not previously associated with a specific vaccine will require other approaches, including epidemiological studies to identify the frequency, distribution and presentation of an event, and to investigate whether an event is associated with vaccination.

GACVS also emphasized that AEFI surveillance systems must be strengthened at country level and regional level to improve the reporting of safety signals following immunization.

Full report of GACVS meeting of 15-16 June 2011, published in the WHO Weekly Epidemiological Record on 22 July 2011