Assessing vaccine safety within Ontario's Universal Influenza Immunization Program, 2012-2013 to 2014-2015

Area of Science:

• Public Health
• Immunization Safety
• Vaccine Surveillance

Background:

• Influenza vaccines are crucial for preventing illness and death.
• Post-marketing surveillance of adverse events following immunization (AEFIs) is vital for vaccine safety monitoring and public trust.

Purpose of the Study:

• To analyze adverse events following immunization (AEFIs) reported after influenza vaccine administration in Ontario.
• To assess the safety profile of influenza vaccines within a universal immunization program.

Main Methods:

• Extracted AEFI data from the Integrated Public Health Information System (iPHIS) for influenza vaccines administered between September 2012 and August 2015.
• Calculated reporting rates using population estimates and distributed doses, applying World Health Organization definitions for serious AEFIs.

Main Results:

• Over 12.1 million doses of influenza vaccine were distributed, with 528 AEFIs reported.
• The overall reporting rate was 4.4 per 100,000 doses, showing a decreasing trend over time. Children under four had the highest population-based reporting rate.
• Injection site reactions were the most common AEFIs (36.2%), followed by allergic skin reactions (21.1%) and rashes (17.3%). Serious AEFIs were rare (1.6 per million doses).

Conclusions:

• Influenza vaccines administered in Ontario demonstrated a low rate of reported adverse events.
• The majority of reported events were mild and self-limiting, consistent with a favorable safety profile.
• Findings support the continued use and safety of influenza vaccines in public health programs.