Multi-mode spatial accessibility to vaccination services and its impact on influenza-related hospitalisations among older adults

BACKGROUND: Although influenza vaccines are available free of charge to older adults in Beijing (China), coverage remains low. Limited spatial accessibility to vaccination services may be an important contributing factor. We quantified spatial accessibility to points of vaccination (PoVs) and examined its association with acute respiratory infection (ARI)-related hospitalisations among older adults. METHODS: We used high-resolution, real-time travel data to quantify spatial accessibility to PoVs by walking, driving, and public transport, incorporating variation by day of week and time of day, at the jiedao (subdistrict) level. Negative binomial regression models examined associations between accessibility and ARI-related hospitalisations among older adults across three influenza seasons (2016-2019), adjusting for confounders. RESULTS: Weekend accessibility was substantially worse than weekday accessibility, with 56.4% of jiedaos experiencing >30 min of additional travel time. Better accessibility was associated with lower ARI-related hospitalisations. Incidence rate ratios were 0.76 (95% CI: 0.61-0.95), 0.73 (95% CI: 0.59-0.90), and 0.60 (95% CI: 0.47-0.76) across three influenza seasons. Model estimates suggest that ensuring all jiedaos have accessible PoVs could avert 1300-3500 ARI-related hospitalisations annually, corresponding to USD 3-8 million in direct medical cost savings per season. DISCUSSION: Spatial accessibility to vaccination services remains a barrier to vaccine uptake in urban settings. The presence of facilities alone does not ensure access, particularly for older adults reliant on others for travel. Improved accessibility is linked to lower ARI-related hospitalisations and could reduce healthcare burden. Expanding PoVs (e.g. by extending weekend hours) may help close this gap.