AEFIs

AEFIs stands for adverse events following immunization. It refers to any medical occurrence after vaccination that is temporally related to immunization; it does not necessarily indicate that the vaccine caused the event. Most AEFIs are mild, common reactions such as pain at the injection site, swelling, fever, irritability, or fatigue. Serious AEFIs are rare and require careful evaluation to determine whether the vaccine contributed to the event.

Causality assessment aims to distinguish coincidental events from vaccine-related ones. This process considers temporality, biological plausibility, existing evidence from studies, and the exclusion of alternative explanations. Standardized definitions, such as those from the Brighton Collaboration, support consistent classification of adverse events for surveillance and research.

Safety monitoring relies on both passive and active systems. In many countries, spontaneous reports from clinicians, patients, or manufacturers feed national databases (for example, VAERS in the United States, the Yellow Card scheme in the United Kingdom, and similar systems in other regions). Active surveillance programs actively seek data and may provide more robust incidence estimates. Internationally, the WHO Program for International Drug Monitoring maintains VigiBase, a global repository of adverse-event reports.

The objective of AEFI surveillance is to detect safety signals, evaluate causal relationships, inform vaccination policy, and guide risk communication. Vaccines remain overwhelmingly beneficial, preventing serious disease and death; AEFIs are typically far fewer in number and less severe than the illnesses vaccines prevent. Management emphasizes prompt care for serious events and transparent reporting to maintain public trust.