[2021-2022 Influenza and Respiratory Viruses Laboratory Surveillance Report in the Republic of Korea]

The surveillance of influenza and respiratory viruses was conducted from 36 weeks in 2021 to 35 weeks in 2022. Respiratory specimens were collected from patients with influenza in 77 private clinics. During the 2021-2022 flu season, 5,959 specimens were collected; the diagnosis was made using multiplex RT-PCR. Findings indicated that 38 cases were positive for influenza. All these cases were confirmed to be infections with influenza A(H3N2) and were genetically and antigenically similar to the strains observed in the 2021-2022 and 2022-2023 seasons. Additionally, all isolated influenza viruses were susceptible to neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir). During this period, rhinovirus had the highest incidence (21.8%), followed by the respiratory syncytial virus (11.3%), parainfluenza virus (10.5%), bocavirus (5.1%), adenovirus (4.6%), human coronavirus (3.3%), and metapneumovirus (0.4%). In the 2020-2021 season, the influenza virus was not detected; however, in the 2021-2022 season, it was consistently at a low activity after 27 weeks. Further, among respiratory viruses, the detection rate of enveloped viruses increased, unlike during the 2020-2021 season, when non-enveloped viruses (rhinovirus, adenovirus, and bocavirus) were prevalent. It is presumed that changes in various quarantine policies, increase in social activities, and low herd immunity due to low morbidity of other respiratory infectious diseases during the coronavirus disease 2019 outbreak influenced the increased detection of influenza and respiratory viruses. Accordingly, we will continue to monitor changes in outbreaks closely and analyze virus characteristics through the Korea Respiratory Virus Integrated Surveillance System.