The document discusses causality assessment of adverse events following immunization (AEFI). It explains that prior to assessment, information on the AEFI is required. A formal assessment involves a national expert committee reviewing cases systematically using criteria like time, severity, and biological plausibility to determine if the AEFI was very likely, probable, possible, unlikely, or unrelated to vaccination. The committee needs independence, expertise, and clear processes to conduct high quality assessments and ensure program credibility. Serious AEFIs, clusters, signals, and events causing concern should be selected for in-depth review.

1. How is Causality Assessment done? WHO

12. Assessment of Routine and Serious AEFIs Previous knowledge Clinical characteristics Lab findings Data quality Likelihood/exclusion of other causes CAUSALITY Association (time, place ) Biological Plausibility Temporal Relation Consistency Reproducibility Reliability Specificity and Strength of Association Rx, risk factors, susceptibility, program error Concomitant or Preceding Conditions Confident diagnosis of lesion lab results favour causation Previously Known Reaction

13. Sample format for causality assessment case review

26. Categories of Causality using WHO Causality Assessment Criteria Very likely Probable Possible Vaccine reaction Injection Reaction Programmatic error Coincidental events Unclassifiable Insufficient evidence to classify Unlikely Unrelated

27. Causality of Passive AEFI Serious Reports (ACCA review, Canada, 1994-1999) When data quality and/or quantity are poor or limited; causality assessment NOT possible 25.8% 92 Unclassifiable 33.3% 24.7% 88 Unrelated 21.2% 15.7% 56 Unlikely 22.0% 16.3% 58 Possible 11.7% 8.7% 31 Probable 11.7% 8.7% 31 Very likely Proportion Of Evaluated Proportion of Total Number

29. EPIDEMIOLOGICAL STUDIES Adverse event Yes No Total Vaccine Yes a b a+b No c d c+d Auriche M, Loupi E. Drug Safety 1993; 9 (3): 30-35 Risk ratio= Risk in vaccinated: A/A+B Risk in unvaccinated: C/C+D