The age-specific impact of COVID-19 vaccination on medical expenditures and hospitalization duration after breakthrough infection: The Vaccine Effectiveness, Networking, and Universal Safety (VENUS) Study

Objectives Although COVID-19 no longer constitutes a Public Health Emergency of International Concern, vaccination remains an important tool for reducing disease burden and mitigating future outbreaks. However, little is known about the impact of vaccination on medical expenditures and hospitalization duration after breakthrough infection. This study aimed to examine this impact during the Delta wave in Japan. Methods This retrospective study was conducted using medical care claims data, vaccination records, and COVID-19-related information. COVID-19 cases in three municipalities were categorized into two age groups: 20–64 years and ≥65 years. For each group, we constructed linear regression models with a generalized estimating equation. We calculated the risk ratios (RRs) and 95% confidence intervals (CIs) of COVID-19 vaccination for total medical expenditures and hospitalization duration after adjusting for sex, comorbidities, and municipality. Results We analyzed 618 cases aged 20-64 years (mean age: 38.4 years, women: 45.1%) and 208 cases aged ≥65 years (76.4 years, 53.8%). The RRs (95% CIs) of vaccination for total medical expenditures were 0.53 (0.44–0.64) in the 20-64 years age group and 0.51 (0.39–0.66) in the ≥65 years age group. Next, the RRs (95% CIs) of vaccination for hospitalization duration were 0.59 (0.42–0.83) in the 20–64 years age group and 0.69 (0.49–0.98) in the ≥65 years age group. Conclusions COVID-19 vaccination was associated with lower total medical expenditures and hospitalization duration after breakthrough infection, with a more pronounced effect in older persons.