Vaccine-Preventable Hospitalizations Increase in Mental Health Service Users

Admission to a hospital for a vaccine-preventable condition is 3.2 times more likely to occur among mental health (MH) service users in New South Wales, Australia than all other residents in the population, and MH service users incurred 3.8 times more hospital bed days than other residents, according to study findings published in Psychological Medicine.

Premature death, avoidable hospitalizations, and increased rates of preventable and chronic medical conditions face people living with mental illness. There are many vaccine-preventable conditions (COVID-19, pneumonia, hepatitis, influenza) that may foster illness and death. Investigators assessed the variation by sex, age, and socioeconomic disadvantage among mental health service users for the risk of hospitalization for many vaccine-preventable conditions.

They conducted a population-based retrospective, observational study using linked data from New South Wales (NSW), Australia that included adult MH service users (n=418,915; 52% women; 84% 18-64 years of age) and the balance of the adult NSW adult population (n=6,162,602; 51% women; 79% 18-64 years of age) from July 2015 through June 2020 that detected vaccine-preventable hospitalizations (VPH) for 19 conditions. They defined the MH service users (aged 18 to 100 years) as NSW residents with any public community MH contact or MH hospitalization from July 2013 through June 2020. They defined MH hospitalizations as at least 1 day in a designated MH unit or receiving care for a primary diagnosis of a nonorganic MH condition in a private or public hospital. Age was estimated at the study-period midpoint. Incident rate ratios were adjusted for sex, age, and disadvantage.

At first VPH admission, other NSW residents were 9 years older (mean age) than MH service users. Vaccine-preventable pneumonias represented the largest age gap (11 to      13 years older). MH service users 35 to 64 years of age had the highest relative risk of VPH. The highest risk of admission for hepatitis B among MH service users were 35 to 54 years of age.

Overall, investigators found 94,180 VPH (41% influenza, 33% hepatitis, 10% herpes zoster) and the adjusted incidence rate ratio (aIRR) for VPH admissions were significantly higher among MH service users vs all NSW residents (aIRR, 3.2; 95% CI, 3.1-3.3). Relative risks were higher for all conditions measured including COVID-19 (supplementary analysis conducted July 2020 to September 2021) (aIRR, 2.0; 95% CI, 1.9-2.2) and risks were highest for hepatitis B (aIRR, 4.4; 95% CI, 4.3-4.6), streptococcal pneumonia (aIRR, 3.6; 95% CI, 3.3-3.9) and whooping cough (aIRR, 3.1; 95% CI, 2.3-4.2).

After adjusting for sex, age, and socioeconomic disadvantage, MH service users vs other NSW residents were 2.6 times more likely to undergo a VPH. Average hospital length of stay for VPH of 9.7 days (MH service users) vs 8.1 days (other NSW residents) combined with this higher hospitalization rate shows MH service users undergoing 3.8 times more hospital bed days per capita vs other NSW residents (95% CI, 3.77-3.82).

Study limitations include the inability to examine the relationship between vaccination status vs increased hospitalization rates, no data on community MH service contacts with private MH or primary care providers, no prescription medication data, community MH records lacking diagnostic information, and no data on the COVID-19 Omicron variant wave.

“MH service users have increased risk of hospitalization for many vaccine-preventable conditions,” investigators concluded. They added, “This may be due to reduced vaccination rates, more severe illness requiring hospitalization, greater exposure to infectious conditions, or other factors.” They urge the prioritization of vaccination strategies for people living with mental illness.