Association of COVID-19 vaccination with improved treatment adherence in patients with schizophrenia: A propensity score-matched cohort study.

People with schizophrenia are a high-priority group for COVID-19 vaccination. However, large-scale data on the real-world clinical impact of vaccination in this vulnerable population is limited. We aimed to evaluate the association of COVID-19 vaccination with treatment adherence, psychiatric stability, and SARS-CoV-2 infection risk in patients with schizophrenia. We conducted a nationwide, retrospective, propensity score-matched cohort study (study period: December 1, 2019-December 31, 2022) using linked data from the National Health Insurance Service and Korea Disease Control and Prevention Agency databases in South Korea. We identified patients with schizophrenia aged 19-64 years and stratified them into vaccinated (three doses) and unvaccinated groups. A 1:1 propensity score matching was performed. The primary outcomes were schizophrenia-related hospitalization and emergency department visits. Key secondary outcomes included medication adherence and diagnosed SARS-CoV-2 infection. The study cohort comprised 4629 pairs (N = 9258). No significant between-group differences were observed in the rates of schizophrenia-related hospitalization or emergency department visits. The vaccinated group showed a significantly smaller decline in medication adherence compared with the unvaccinated group. Counter-intuitively, the vaccinated group had a significantly higher rate of diagnosed SARS-CoV-2 infection, a finding most plausibly attributable to ascertainment bias rather than reduced vaccine efficacy. COVID-19 vaccination was not associated with psychiatric destabilization but was associated with significantly improved treatment adherence. Our study indicates that vaccination may play a supportive role in maintaining clinical continuity for individuals with schizophrenia.