An Outbreak of Breakthrough Infections by the SARS-CoV-2 Delta Variant in a Psychiatric Closed Ward

ABSTRACT

Background@#A rapid decline in immunity and low neutralizing activity against the delta variant in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinees has been observed. This study describes an outbreak of coronavirus disease 2019 (COVID-19) breakthrough infections caused by the SARS-CoV-2 delta variant in a psychiatric closed ward. @*Methods@#Data from epidemic intelligence service officers were utilized to obtain information regarding demographic, vaccination history, and clinical data along with SARSCoV-2 PCR test results for a COVID-19 outbreak that occurred in a closed psychiatric ward. @*Results@#Among the 164 residents, 144 (87.8%) received two doses of vaccines, with 137 (95.1%) receiving two doses of ChAdOx1 nCoV-19 vaccine. The mean interval between the second dose of vaccine and COVID-19 diagnosis was 132.77 ± 40.68 days. At the time of detection of the index case, SARS-CoV-2 had spread throughout the ward, infecting 162 of 164 residents. The case-fatality ratio was lower than that in the previously reported outbreak before vaccines were available (1.2%, 2/162 vs. 6.9%, P = 0.030). Prolonged hospitalization occurred in 17 patients (11.1%) and was less prevalent in the vaccinated group than in the unvaccinated group (8.5% vs. 25.0%, P = 0.040). @*Conclusion@#The findings of this study highlight that while vaccination can reduce mortality and the duration of hospitalization, it was not sufficient to prevent an outbreak of the SARSCoV-2 delta variant in this psychiatric hospital setting.