Impact of Repeated Vaccination on 2017-2018 Influenza Vaccines Effectiveness – A Retrospective Study
Influenza causes seasonal illness characterized by fever, myalgia and respiratory symptoms which can lead to hospitalization and death. Although it is a vaccine preventable disease, influenza contributes directly and indirectly to a large number of hospitalizations and outpatient visits. More specifically, influenza causes every year approximately 12,000 hospitalizations and 3,500 deaths in Canada, of which 90% occur in people 65 years and older. Recently, numerous studies have investigated the impact of repeated vaccination on its effectiveness reporting a large variety of results. Our goal is to evaluate the impact of repeated vaccination on influenza vaccine effectiveness to reduce the risk of laboratory-confirmed infection, healthcare utilization, antimicrobial use and cardiovascular events in vaccinated individuals compared to unvaccinated individuals. Therefore, our results will inform policy decision makers on the effectiveness of the vaccination program to reduce public health burden during influenza season.