Vaccine-preventable hospitalisations in adult mental health service users: A population study

Background Vaccine-preventable conditions cause preventable illness and may increase mortality in people living with mental illness. We examined how risks of hospitalisation for a wide range of vaccine-preventable conditions varied by age and sex among mental health (MH) service users. Methods Linked population data from New South Wales (NSW), Australia were used to identify vaccine-preventable hospitalisations (VPH) for 19 conditions from 2015 to 2020. Adult MH service users (n = 418 915) were compared to other NSW residents using incidence rates standardised for age, sex and socioeconomic status. Secondary analyses examined admissions for COVID-19 to September 2021. Results We identified 94 180 VPH of which 41% were influenza, 33% hepatitis B and 10% herpes zoster. MH service users had more VPH admissions [adjusted incidence rate ratio (aIRR) 3.2, 95% CI 3.1-3.3]. Relative risks were highest for hepatitis (aIRR 4.4, 95% CI 4.3-4.6), but elevated for all conditions including COVID-19 (aIRR 2.0, 95% CI 1.9-2.2). MH service users had a mean age of 9 years younger than other NSW residents at first VPH admission, with the largest age gap for vaccine-preventable pneumonias (11-13 years younger). The highest relative risk of VPH was among MH service users aged 45-65. Conclusions MH service users have increased risk of hospitalisation for many vaccine-preventable conditions. This may be due to reduced vaccination rates, more severe illness requiring hospitalisation, greater exposure to infectious conditions or other factors. People living with mental illness should be prioritised in vaccination strategies.