Associations between income changes and the risk of herpes zoster: LIFE study

Economic stability is thought to be associated with health outcomes. Income changes may affect the occurrence of herpes zoster (HZ), which is a neurocutaneous disease caused by the varicella-zoster virus. This retrospective cohort study aimed to examine the associations between annual income changes and incident HZ in a Japanese population. The analysis was conducted using a database of public health insurance claims data linked with administrative data containing income levels. The study population comprised 48,317 middle-aged persons aged 45-64 years from five municipalities, and participants were followed-up from April 2016 until March 2020. Income changes were categorized as income unchanged (income in the year of interest remained within 50% of income in the previous year), income rise (income increased by more than 50% from the previous year to the year of interest), and income drop (income decreased by more than 50% from the previous year to the year of interest). Cox proportional hazards regression analyses were performed to calculate the hazard ratios of HZ for income drop and income rise (reference: income unchanged) as time-varying variables. Covariates included age, sex, and immune-related conditions. The results showed that income drop was significantly associated with a higher hazard ratio (1.15, 95% confidence interval: 1.00-1.31) for HZ. In contrast, income rise was not associated with HZ. A subgroup analysis revealed that the lowest baseline income group had a significantly higher risk of HZ when experiencing an income drop (HR: 1.56, 95% CI: 1.13-2.15). As zoster vaccination is voluntary and vaccination coverage in middle-aged persons is low in Japan, our findings indicate that it may be advantageous to promote and subsidize voluntary vaccinations for middle-aged people with low baseline income who have experienced substantial income reductions in order to reduce the risk of HZ.