What is an adverse event following immunization (AEFI)?

An adverse event following immunization (AEFI) is defined as any medical occurrence after vaccination that may be linked to the vaccine. This encompasses a broad spectrum of events, ranging from mild side effects, like fever or soreness at the injection site, to more serious reactions that may arise even if they are not directly caused by the vaccine itself. The key aspect is the temporal relationship to vaccination, meaning these events occur after the vaccine is administered and are reported to help monitor vaccine safety.

The importance of this definition lies in its inclusive nature, allowing for the monitoring of all potential health outcomes post-vaccination. This is critical for public health surveillance and ensuring the safety of vaccines, as it encourages reporting of a wide range of events, which can be analyzed for patterns that might indicate issues with specific vaccines.

Other options outline more specific scenarios or limitations that do not capture the full scope of what an AEFI entails. For instance, documenting only side effects experienced during the vaccination process misses events that could occur afterward. Similarly, focusing solely on severe reactions requiring hospitalization or those occurring immediately after vaccination confers an unnecessarily narrow view of adverse events, neglecting the more common, less severe reactions that still warrant monitoring and reporting.