Validating sociodemographic disparities in HPV vaccine uptake in a universal, publicly funded, low barrier, school-based immunisation program in the Vancouver Coastal Health region of British Columbia, Canada: A cross-sectional study

OBJECTIVES: Exploratory analysis conducted with the 2021/2022 age-eligible school cohorts identified lower vaccine coverage among grade 6 and 9 students of the Vancouver Coastal Health (VCH) region who were residing in neighbourhoods facing material and social deprivation. Other determinants of lower coverage included male sex, attendance in non-faith-based independent school category, and residence in rural areas. This study aimed to replicate the analysis in the 2022/2023 cohort to assess reliability across school years less affected by the pandemic and prioritise the determinants in order to implement programmatic actions to improve HPV vaccine uptake. METHODS: We conducted a cross-sectional study of grade 6 and 9 students residing in the VCH region and attending VCH schools. A cross-classified multilevel model was developed to replicate and validate findings from the 2021/2022 cohort, describing associations between sociodemographic explanatory variables and underimmunisation. Public health priorities were informed by population attributable fractions (PAFs) from the final model. RESULTS: The final model confirmed significant associations between immunisation coverage and grade, geographic area of residence, school category, and social deprivation. Students residing in the most socially deprived areas (Q4 and Q5) had 32% (PAF = 5.3%) and 70% (PAF = 7.0%) higher odds, respectively, of being underimmunised compared to those residing in the least socially deprived areas. Students residing in socially deprived Q4 and Q5 neighbourhoods were enrolled in the majority (93%) of schools, those underimmunised were enrolled in 82% of schools, and 38 schools (11.8%) enrolled 10 or more underimmunised students. Based on these results, the baseline program was strengthened in all schools, and 38 schools were prioritised to receive enhanced public health interventions. CONCLUSIONS: This study confirmed previously reported associations, namely the relationship between social deprivation and underimmunisation, and underscores the need for targeted outreach to socially vulnerable families within the context of a publicly funded school immunisation program.