WHO AEFI: Global Pharmacovigilance
How the WHO coordinates global adverse event following immunization surveillance
The WHO's Adverse Events Following Immunization (AEFI) surveillance system coordinates global vaccine safety monitoring. Through international collaboration, the WHO helps member states detect, investigate, and respond to vaccine safety signals that may have international implications.
How WHO AEFI Surveillance Works
- National surveillance: Individual countries collect and investigate AEFI reports
- Regional pharmacovigilance centers: WHO Regional Offices (EURO, AMRO, AFRO, etc.) coordinate at regional level
- Global database: Reports feed into VigiBase — the WHO Global Individual Case Safety Reports database
- Signal detection: WHO experts analyze global data for potential safety signals
- International investigation: Coordinated responses to signals with global implications
VigiBase: The Global Database
Managed by the Uppsala Monitoring Centre (Sweden), VigiBase contains over 30 million adverse event reports from more than 170 countries. Key features:
- Standardised data format (CIOMS and MedDRA)
- WHO-ART terminology for vaccine adverse events
- Comprehensive global coverage
- Public access to summary statistics
Classification of AEFIs
WHO classifies AEFIs into 5 categories:
Vaccine Product-Related Reaction
Caused or precipitated by the active component or another component of the vaccine.
Vaccine Quality Defect-Related Reaction
Caused by a vaccine that is defective in quality, including its administration device as provided by the manufacturer.
Immunization Error-Related Reaction
Caused by inappropriate vaccine handling, prescribing, or administration — preventable by nature.
Immunization Anxiety-Related Reaction
Arising from anxiety about the immunization, not from the vaccine itself. Examples include vasovagal episodes.
Coincidental Event
Caused by something other than the vaccine or immunization process. Would have occurred regardless of vaccination.
Global Signal Investigation Process
- Data mining of global database to assess signal strength
- Consultation with national pharmacovigilance centers
- Epidemiological studies in multiple countries
- Assessment by WHO Global Advisory Committee on Vaccine Safety (GACVS)
- Updated guidance to member states and vaccine manufacturers
Key Global Investigations
- Dengue vaccine (Dengvaxia): Identified increased severe dengue in seronegative recipients — led to major label restrictions
- COVID-19 vaccines: Coordinated global monitoring of myocarditis and TTS signals
- Rotavirus vaccines: International surveillance for intussusception
- HPV vaccines: Global monitoring for autoimmune conditions
Limitations
- Variable data quality across member states
- Underreporting common especially in low-resource settings
- Difficulty establishing causality from aggregate international data
- Different healthcare systems affect reporting patterns
Sources & Citations
WHO. "Pharmacovigilance." World Health Organization. https://www.who.int/teams/regulation-prequalification/regulation-and-safety/pharmacovigilance
WHO. "AEFI Surveillance Guidelines." World Health Organization. https://www.who.int/publications/i/item/9789241507455
WHO. "Global Advisory Committee on Vaccine Safety (GACVS)." World Health Organization. https://www.who.int/groups/global-advisory-committee-on-vaccine-safety
Uppsala Monitoring Centre. "VigiBase." WHO Collaborating Centre for International Drug Monitoring. https://www.who-umc.org/vigibase/vigibase/