Abstract
Patients with mental illnesses are more susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and are more likely to develop severe disease when infected. Therefore, in many countries, they have been considered a priority group for vaccination. However, the immunological effects of vaccination in these patients remain insufficiently studied. In this study, we investigated changes in serum neutralizing antibody titers against SARS-CoV-2 over a two-year period. Fifty-three participants who had experienced a coronavirus infection (COVID-19) outbreak in a closed psychiatric ward in September 2020 were followed. Antibody titers were measured after natural infection and subsequent vaccination. Neutralizing antibody titers declined over time, and 20% of patients fell below the positivity threshold within six months after infection. In contrast, all patients who received two subsequent mRNA vaccinations maintained high antibody titers for at least six months after vaccination. These findings suggest that vaccination provides effective and sustained humoral immunity in psychiatric patients with a history of COVID-19 infection.