Causality assessment of an adverse event following immunization (‎AEFI)‎: user manual for the revised WHO classification, 2nd ed., 2019 update

Overview

Since the 2013 publication of the “Causality assessment of an adverse event following immunization (AEFI), user manual for the revised WHO classification”, there has been extensive global interest in adopting the new revised causality assessment methodology for vaccine pharmacovigilance systems. WHO provided technical support and helped build capacity in countries of all WHO Regions who wanted to use the revised methodology. An AEFI causality assessment software was developed, translated to six UN languages and made available online.

Recently, the new methodology has been scientifically evaluated. In April 2017, WHO coordinated an India - Zimbabwe project entitled “Inter-country study to assess the inter-rater reliability of the WHO AEFI causality assessment methodology and the utility of the new WHO AEFI causality assessment software”. The quantitative aspect of the study determined that there was realistic agreement between assessors in their findings. The qualitative aspect of the study identified areas of the methodology that could be made even more robust by the use of more accurate and clearer language, semantics and graphics.

In the meanwhile, feedback from surveillance systems and other research studies have shed new evidence on areas such as, “substandard and falsified vaccines”, “immunization anxiety” and “immunization stress related responses” that need to be incorporated into new guidance documents.