Under recommended conditions, all vaccines used in national immunization programmes are safe and effective if used correctly. In practice, however, no vaccine is completely risk-free and adverse events can occasionally result after an immunization.

Adverse events can range from minor adverse effects to more severe reactions. They can be a cause of public concerns about vaccine safety. To understand a specific event and to be able to respond appropriately, there are several questions that you need to answer:

  • What caused the event?
  • Was it related to the vaccine or the way it was administered, or was it unrelated?
  • Is the event serious?

This module will help you to answer these questions. You will learn the difference between adverse event and adverse reaction and you will look at the main types of adverse events and the situations in which they may occur. You will also be introduced to the challenges and opportunities of mass vaccination campaigns. Because of the nature of these campaigns, adverse events may be more noticeable.

Module outcomes

By the end of this module you should be able to:

  • 1define the main types of adverse events following immunization (AEFIs);
  • 2differenciate between event and reaction;
  • 3differentiate between serious and severe reactions, and between minor and severe reactions;
  • 4describe potential underlying causes for each type of AEFI, and understand the link between the AEFI and its cause;
  • 5summarize the expected incidence of the different types of AEFI.