Epidemiological Shifts in Respiratory Virus Infections Among Older Adults (≥65 Years) Before and After the COVID-19 Pandemic: An 18-Year Retrospective Study in the Republic of Korea

We investigated respiratory virus epidemiology in older adults across pre-pandemic (2007-2019), pandemic (2020-2022), and post-pandemic (2023-2024) periods, focusing on how public health interventions shaped surveillance, prevalence, and sex-specific trends. We conducted a retrospective cross-sectional study at a 1000-bed tertiary hospital in the Republic of Korea during 2007-2024, analyzing 4692 nasopharyngeal swab specimens collected from adults aged ≥ 65 years with suspected respiratory infections during 2007-2024. The specimens were tested for 15 respiratory viruses using multiplex real-time polymerase chain reaction. The outcomes included virus-specific detection rates and seasonal, sex-based and temporal trends before and after the COVID-19 pandemic. During the pre-pandemic period, older adults accounted for 13.2% of the tested individuals, which significantly increased to 52.0% in the later periods. <i>Influenza A</i> was the most frequently detected virus, followed by rhinovirus and human metapneumovirus. <i>Influenza, RSV A/B</i>, and <i>coronaviruses 229E</i> and <i>OC43</i> showed peak positivity in winter, <i>parainfluenza virus type 3</i> peaked in summer, and <i>rhinovirus</i> circulated year-round. Virus circulation was markedly suppressed during 2020-2022 and partially rebounded during 2023-2024. This study highlights the shift in diagnostic access and epidemiologic patterns of respiratory virus infections in older adults following the COVID-19 pandemic.