The Association between Prior Seasonal Influenza Vaccination and Subsequent Seasonal Influenza Vaccine Effectiveness in Canada
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Influenza is a major burden to the health of thousands of Canadians every year. Recent observational studies have suggested that prior influenza vaccination could impact subsequent influenza vaccine effectiveness (VE) under some circumstances. This study investigates the association between prior influenza vaccination and subsequent seasonal influenza VE in three influenza seasons in Canada (2011-2014). Using a test-negative control design, the Canadian Immunization Research Network’s (CIRN) Serious Outcomes Surveillance (SOS) network prospectively identified cases and matched controls from each study season using active influenza surveillance in hospitals. Overall, results of conditional logistic regression analyses provide some evidence for an association between prior influenza vaccination and subsequent influenza VE in Canada. This association varied depending on the strain and season under observation. Future prospective studies to examine this association and to explore contributing biological and immunological mechanisms are critical to inform influenza immunization policy in Canada.