[The Suspected Coronavirus Disease 2019 Reinfection Cases and Vaccine Effectiveness, The Republic of Korea].

As the coronavirus disease 2019 pandemic continues, the suspected reinfection cases are increasing due to the decrease in immune antibodies and immune avoidance reactions to new variants. We analyzed the characteristics of suspected reinfection cases identified by the surveillance system from January 20, 2020 to July 22, 2023. Moreover, we assessed the vaccination history to evaluate vaccine effectiveness. Among the suspected reinfection cases (7.8%), second infected cases were 98.5%, third infected cases were 1.4%, and more than fourth infected cases were 0.02%. Secondary infections almost were in the Omicron waves, especially with members of long-term care facilities during the Omicron variant period (5.9%) higher than the pre-Omicron period (1.6%). The fatality rate of the second infected cases (0.06%) was lower than the fatality rate of the one-time infected cases (0.12%). The critical infection rate of second infected cases aged 60 or older was 0.54% and the fatality rate was 0.29%. Among second infected cases aged 60 or over, the vaccine effectiveness against critical infection compared to unvaccinated was 68.4% for monovalent vaccine, 77.1% for bivalent vaccine, and the vaccine effectiveness against death compared to unvaccinated was 69.7% for the monovalent vaccine, 81.2% for the bivalent vaccine. Therefore, even in the suspected reinfection cases with the history of previous infection, it is necessary to recommend regular vaccinations to prevent severity and death for the elderly group with a high fatality rate.