Impact of the universal seasonal influenza vaccination policy in the province of Manitoba, Canada: A population-based, province-wide record-linkage study

Introduction: In 2010, the government of the province of Manitoba, Canada introduced universal seasonal influenza vaccination policy (USIVP), providing free-of-charge vaccination to all registered residents of the province at least six months of age. Impact of the policy on seasonal influenza vaccine (SIV) uptake (receipt of vaccine) in Manitoba remains unclear, as there is a lack of published evaluations.Methods: We conducted an ecological study, utilizing population-wide data from several linked de-identified Manitoba Health and Seniors Care administrative health databases. The study period was from 2000/ 01-2019/20 influenza seasons. The primary exposure was USIVP (five influenza seasons pre-policy [2005/ 06-2009/10] compared with post-policy [2010/11-2014/15]). The outcome was SIV uptake. We conducted pre/ post logistic regression analysis stratified by age group (<5-, 5-17-, 18-44-, 45-64-, >= 65-year-olds) and certain population socioeconomic and health-related characteristics. Results are adjusted odds ratios with associated 95 % confidence intervals.Results: We observed significantly increased adjusted odds of SIV uptake post-policy relative to pre-policy in all age groups except >= 65-year-olds already covered from inception of the vaccination programme. The adjusted odds ratios ranged from 0.76 (0.75-0.76) among >= 65-year-olds to 2.15 (2.13-2.18) among 5-17-year-olds, and were largely homogeneous within age groups across sex, income quintiles, regions of residence, and categories of number of visits to primary care physician/hospitalization one year prior to an influenza season except among <5-and 5-17-year-olds. These findings were mostly consistent irrespective of sex and region of residence although there was variability across income quintiles in Northern Manitoba region.Conclusions: Introduction of the USIVP in Manitoba was followed by a significant increase in SIV uptake in the five years post policy among <65-year-olds, with similar increased relative odds of vaccination observed within age groups across subpopulations. The observed variations in the relative odds of vaccination across income quintiles in Northern Manitoba region requires administrative attention.