Characteristics of COVID-19 outbreaks and risk factors for transmission at an army training center in South Korea from June to August 2021.

OBJECTIVES: It is crucial to establish the characteristics of coronavirus disease 2019 (COVID-19) outbreaks at army training centers to develop preventive measures. Therefore, this study aimed to determine the COVID-19 transmission patterns and risk factors in a sequence of outbreaks at an army training center from June to August 2021. METHODS: This study included 1,324 trainees at an army training center where outbreaks occurred from June to August 2021. The outbreak was qualitatively analyzed according to the period, attack rate, demographic characteristics, vaccination history, and living areas. An aerodynamic experiment was performed to evaluate aerosol transmission in living areas. RESULTS: Three outbreaks occurred at the army training center from June to August 2021. The first, second, and third outbreaks lasted for 32, 17, and 24 days, and the attack rates were 12.8%, 18.1%, and 8.9%, respectively. Confirmed cases were distributed in all age groups. Recruits and the unvaccinated were at higher risk for COVID-19. The aerodynamic experiment verified the possibility of aerosol transmission within the same living area. CONCLUSION: COVID-19 transmission at army training centers should be minimized through quarantine and post-admission testing during the latency period as part of integrated measures that include facility ventilation, vaccination, indoor mask-wearing, and social distancing.

An outbreak of SARS-CoV-2 reinfection in a long-term care facility in South Korea.

We report a cluster of 12 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection in a long-term care facility in South Korea. There were two outbreaks of SARS-CoV-2 infection in the facility at the beginning and end of October 2021, respectively. All residents in the facility were screened for SARS-CoV-2 infection using RT-PCR as part of the investigation of the second outbreak. Twelve residents, who had infection confirmed during the first outbreak, were found to be re-positive for RT-PCR test at the second outbreak. 8 Of 12 RT-PCR re-positive cases were confirmed as reinfections based on investigation through the whole genome sequencing, viral culture, and serological analysis, despite of the short interval between the first and second outbreaks (29-33 days) and a history of full vaccination for 7 of the 12 re-positive cases. This study suggests that decreased immunity and underlying health condition in older adults makes them susceptible to reinfection, highlighting the importance of prevention and control measures regardless of vaccination status in long-term care settings.

Reinfection with SARS-CoV-2 in general population, South Korea; nationwide retrospective cohort study.

To better understand the epidemiology of SARS-CoV-2 reinfections, we analyzed national data from South Korean who were followed longitudinally from January 2020 to April 2022. We conducted a nationwide retrospective cohort study to estimate possible SARS-CoV-2 reinfection rates in all residents in South Korea, with at least two episodes of laboratory-confirmed SARS-CoV-2 infection by reverse-transcriptase polymerase chain reaction or rapid antigen test (RAT) performed at least 45 or more days between both episodes, between January 2020 and April 2022. There were 16 130 855 laboratory-confirmed SARS-CoV-2 cases in South Korea, with 55 841 (346.2 per 100 000; or 0.3% of all infections) cases of possible reinfections. The reinfection rate has increased from 6.0 cases per 100 000 during Pre-Delta period to 128.0 cases per 100 000 and 355.1 cases per 100 000 during Delta and Omicron periods, respectively. Persons with one dose of vaccination had the highest reinfection rate of 642.2 per 100 000, followed by unvaccinated persons (536.2/100 000) and two-dose vaccinated persons (406.3/100 000). Our finding suggests that the majority of possible reinfections occurred following the emergence of new variants.