When does Follow-up on Adverse Events Improve the Understanding of Medicine and Vaccine Safety? Insights from Global Expert Perspectives

INTRODUCTION AND OBJECTIVE: Adverse events (AEs) reported with medicines and vaccines form the foundation of pharmacovigilance (PV), enabling the detection, assessment, and prevention of drug-related risks. Initial AE reports often lack relevant clinical detail, limiting their utility. Follow-up is used to obtain additional information but is resource-intensive. Spontaneous reporting systems receive large volumes of reports and follow-up yields additional information in only a proportion of cases. Given these volumes and variable yield, it is important to define when follow-up is most likely to add value and when it is likely to be low-yield or futile. This study aimed to identify scenarios where follow-up on AEs meaningfully improves the understanding of medicine and vaccine safety, and to delineate circumstances when it may be less beneficial or futile. METHODS: A Delphi based methodology was used to systematically gather expert consensus on scenarios in which follow-up of AE reports enhances the understanding of medicine and vaccine safety. RESULTS: Data saturation was achieved after ten interviews. Panel members identified three primary scenarios in which follow-up adds value in PV: supporting causality assessment, strengthening signal detection and monitoring, and informing risk management and public health actions. They saw questionable or no value in follow up of well-characterised labelled events, cases in which the reporter cannot be contacted or did not consent to further contact, and settings where additional data were unlikely to alter benefit-risk. CONCLUSION: This study characterises expert perspectives on when follow-up activities are most likely to provide actionable value. Our results indicate that follow-up improves understanding when it resolves clinical uncertainty, but is inefficient when pursued without regard to impact, supporting a shift to proportionate, purpose-driven follow-up strategies for consistent and efficient use of resources including criteria for prioritisation and de-prioritisation.