The World Health Organization (WHO) runs the largest international drug safety monitoring system in the world. Through its Programme for International Drug Monitoring, the WHO coordinates adverse drug reaction reporting from over 160 countries, feeding into a global database of more than 40 million individual case reports. This system exists to catch safety problems with medicines and vaccines that might not be visible within any single country’s borders.
The WHO Programme for International Drug Monitoring
The WHO Programme for International Drug Monitoring (PIDM) is the backbone of global pharmacovigilance, which is the science of detecting, assessing, and preventing side effects from medicines and vaccines. The program connects national drug safety agencies around the world so they can share reports of suspected adverse reactions. A rare side effect that shows up in five patients scattered across three continents would be nearly impossible to detect if those countries weren’t pooling their data. The PIDM makes that pooling possible.
The operational side of the program is managed by the Uppsala Monitoring Centre (UMC), an independent foundation based in Sweden. UMC was established in 1978 by the WHO and the Swedish government. It functions as a WHO Collaborating Centre, meaning it handles the day-to-day technical work: maintaining the global database, developing analytical tools, and coordinating signal detection across member states. UMC is self-funded and not-for-profit.
VigiBase: The Global Safety Database
VigiBase is the WHO’s global database of reported potential side effects from medicinal products. As of the end of 2024, it contains over 40 million individual case safety reports from more than 160 countries. Roughly 80% of these reports relate to medicines and 20% to vaccines. Reports are coded using standardized terminology systems, including WHODrug (a global dictionary of drug names) and MedDRA (a medical terminology dictionary), so that a side effect reported in Brazil can be meaningfully compared to one reported in Japan.
The sheer scale of VigiBase is what makes it valuable. Many dangerous side effects are rare enough that they don’t surface during clinical trials, which typically enroll thousands of patients. Once a drug reaches millions of people in real-world conditions, new safety patterns can emerge. VigiBase provides the data mass needed to spot those patterns.
How the WHO Detects Safety Signals
A “signal” in pharmacovigilance is a new or previously unrecognized association between a drug and a potential side effect. UMC regularly screens VigiBase using a combination of computerized data mining and manual clinical review. With 40 million reports, automated screening narrows the field, flagging statistical patterns that look unusual. Human experts then evaluate those flagged cases to determine whether the pattern is clinically meaningful or a statistical artifact.
UMC also monitors scientific literature and tracks regulatory actions from national agencies around the world. This parallel monitoring helps identify emerging safety concerns early and prevents multiple organizations from duplicating the same investigation. For assessing whether a single case report suggests a genuine drug-caused reaction, UMC uses a structured causality assessment tool developed in consultation with the PIDM. When evaluating multiple case reports together, analysts apply the Bradford Hill criteria, a well-established framework for judging whether an observed association is likely causal.
Once the evidence is assessed and the scientific literature reviewed, a decision is made about whether the case is strong enough to formally communicate as a signal. Confirmed signals are shared with national regulatory authorities, who can then take action within their own countries, whether that means updating product labels, issuing safety warnings, or restricting use.
Vaccine Safety Oversight
Vaccine pharmacovigilance gets its own dedicated layer of WHO oversight through the Global Advisory Committee on Vaccine Safety (GACVS). This committee conducts risk-benefit assessments for immunization policies being considered by WHO member states. It advises the Strategic Advisory Group of Experts (SAGE), which shapes global immunization recommendations.
GACVS meets on a regular schedule but can also be convened urgently by conference call when a vaccine safety issue of international significance arises. Beyond responding to specific alerts, the committee has taken on a broader capacity-building role. It helped develop the Global Vaccine Safety Blueprint, which is the WHO’s strategy for optimizing vaccine safety worldwide through effective pharmacovigilance. GACVS now advises on specific tools for vaccine safety monitoring, including how adverse events following immunization should be classified, what core data elements every country should collect, and what indicators surveillance systems should track.
Supporting Lower-Income Countries
Pharmacovigilance systems require trained staff, reporting infrastructure, and analytical capacity. Many low- and middle-income countries (LMICs) lack these resources. Rather than pushing every country to build a comprehensive monitoring system from scratch, the WHO developed the Smart Safety Surveillance (3S) strategy, which takes a more targeted approach.
The core idea behind 3S is that countries with limited resources should focus their pharmacovigilance efforts on the products that matter most to them, rather than trying to monitor everything at once. That means prioritizing two categories of medicines: products addressing a high-burden disease specific to the country (such as treatments for sleeping sickness in endemic regions), and new products with limited clinical data that are being introduced simultaneously in wealthy and lower-income countries, where LMICs can’t rely on safety experience from other markets.
The 3S strategy has been implemented across multiple countries including Armenia, Brazil, Ethiopia, India, Peru, and Thailand. Each country selected one or two priority products based on local disease burden and expected use. Interventions varied by country but included training healthcare professionals in adverse event reporting, launching mobile reporting apps, setting up regional sentinel sites at hospitals, and establishing active surveillance protocols. Countries also shared resources with one another. Brazil and Peru, for example, developed a joint regional protocol for active surveillance, while Armenia and Ethiopia collaborated with nongovernmental organizations already doing pharmacovigilance work on the ground.
A key element of 3S is “reliance,” the idea that countries can learn from each other’s regulatory work rather than each one independently reviewing the same data. Study visits between regulatory agencies, shared review of manufacturers’ risk management plans, and cross-border training on analytical tools like VigiFlow and VigiLyze all reduce the burden on any single country’s system.
How Countries Participate
Any WHO member state can join the Programme for International Drug Monitoring by establishing a national pharmacovigilance center and meeting basic requirements for collecting and submitting adverse reaction reports. Once a country joins, its national center collects reports from healthcare professionals and patients, reviews them, and submits them to VigiBase through UMC’s reporting tools. The country retains full ownership of its data and can use the global database to compare its local safety patterns against international trends.
With over 160 countries now contributing data, the network covers the vast majority of the world’s population. This geographic breadth matters because drug safety profiles can differ across populations due to genetic variation, differences in prescribing practices, the presence of counterfeit medicines in certain markets, and interactions with locally prevalent diseases or traditional medicines. A side effect that is common in one population may be rare in another, and only a truly global database can capture that variation.