Adverse events following immunization in Ontario's female school-based HPV program

Area of Science:

• Public Health
• Immunization Safety
• Vaccine Surveillance

Background:

• A school-based human papillomavirus (HPV) vaccination program using the quadrivalent HPV (HPV4) vaccine was implemented for grade 8 girls in Ontario, Canada, starting in September 2007.
• The program aimed to evaluate the safety of the HPV4 vaccine through surveillance of adverse events following immunization (AEFI).

Purpose of the Study:

• To assess adverse events following immunization (AEFI) reports associated with the quadrivalent HPV (HPV4) vaccine administered within the Ontario school-based program.
• To contribute to the comprehensive evaluation of the HPV vaccine program's safety and effectiveness.

Main Methods:

• AEFI reports for the HPV4 vaccine (Gardasil®) administered between September 1, 2007, and December 31, 2011, were extracted from the provincial reportable disease system.
• Confirmed AEFI reports in females aged 12-15 years were included, with events categorized according to provincial case definitions.
• Reporting rates were calculated using the number of vaccine doses distributed as the denominator.

Main Results:

• A total of 133 confirmed AEFIs were reported out of 691,994 HPV4 vaccine doses distributed.
• The overall reporting rate was 19.2 AEFIs per 100,000 doses, with a decreasing trend observed annually.
• Frequently reported events included allergic reactions, rash, and injection site reactions. Ten serious AEFIs were reported, but upon review, anaphylaxis and death reports were not substantiated as vaccine-related.

Conclusions:

• The safety profile of the HPV4 vaccine in this large-scale school-based program is consistent with findings from pre-licensure trials and post-marketing surveillance.
• No new safety signals were identified, notably the absence of venous thromboembolism (VTE) reports in this younger female population.
• Continued monitoring of HPV4 AEFI surveillance data is recommended for ongoing safety assessment and signal detection.