SARS-CoV-2 vaccination prevalence by mental health diagnosis: a population-based cross-sectional study in Ontario, Canada

Abstract

Background: Since the onset of the COVID-19 pandemic, there has been concern about the impact of SARS-CoV-2 infection among individuals with mental illnesses. We analyzed the SARS-CoV-2 vaccination status of Ontarians with and without a history of mental illness.

Methods: We conducted a population-based cross-sectional study of all community-dwelling Ontario residents aged 19 years and older as of Sept. 17, 2021. We used health administrative data to categorize Ontario residents with a mental disorder (anxiety, mood, substance use, psychotic or other disorder) within the previous 5 years. Vaccine receipt as of Sept. 17, 2021, was compared between individuals with and without a history of mental illness.

Results: Our sample included 11 900 868 adult Ontario residents. The proportion of individuals not fully vaccinated (2 doses) was higher among those with substance use disorders (37.7%) or psychotic disorders (32.6%) than among those with no mental disorders (22.9%), whereas there were similar proportions among those with anxiety disorders (23.5%), mood disorders (21.5%) and other disorders (22.1%). After adjustment for age, sex, neighbourhood income and homelessness, individuals with psychotic disorders (adjusted prevalence ratio 1.19, 95% confidence interval [CI] 1.18-1.20) and substance use disorders (adjusted prevalence ratio 1.35, 95% CI 1.34-1.35) were more likely to be partially vaccinated or unvaccinated relative to individuals with no mental disorders.

Interpretation: Our study found that psychotic disorders and substance use disorders were associated with an increased prevalence of being less than fully vaccinated. Efforts to ensure such individuals have access to vaccinations, while challenging, are critical to ensuring the ongoing risks of death and other adverse consequences of SARS-CoV-2 infection are mitigated in this high-risk population.

Figure 1:

Study flow chart. Note: DOLC = date of last contact.

Figure 2:

Relative prevalence^* of partial and no vaccination by (A) diagnostic category and (B) mental health and addiction (MHA) severity. ^*Relative prevalence estimated using modified Poisson regression models, with no mental health disorders as the reference category. Note: cADG = collapsed Aggregated Diagnosis Group.

Figure 3:

Relative prevalence^* of partial and no vaccination by mental health and addiction diagnosis, stratified by health service utilization severity. ^*Relative prevalence estimated using modified Poisson regression models, with no mental health disorders as the reference category. Note: cADG = collapsed Aggregated Diagnosis Group.