Other Important Terms and Definitions

• Serious AEFIs result in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in persistent or significant disability, or is a congenital anomaly or birth defect.
• Non-serious AEFIs do not pose a potential risk to the health of the recipient.
• Clusters are two or more cases of the same or similar events related in time, place/geography, and/or vaccine administered.
• Coincidental events can occur as clusters.
• Immunization stress-related responses can occur in clusters.
• Clusters should be reported.