Long-Term Trends in Respiratory Syncytial Virus A Infections (2007–2024) in Korea

Background/Objectives: Respiratory syncytial virus A (RSV A) is the leading cause of respiratory infections, particularly in vulnerable populations. This study aimed to investigate the long-term epidemiological trends of RSV A infection in the Republic of Korea over an 18-year period (2007–2024), with emphasis on age, sex, and seasonal differences. Methods: A total of 23,284 nasopharyngeal swab specimens were analyzed by multiplex real-time PCR. Statistical comparisons were performed using the chi-square test. Results: The RSV A-positivity rate was highest in 2007 (19.7%) and lowest in 2021 (0.1%) (p < 0.001). Infants (0 years) exhibited the highest infection rate (18.5%, 95% CI: 17.3–19.6), whereas adults aged 20–64 years and older adults showed significantly lower rates (0.7% and 0.9%, respectively). Seasonal peaks occurred in winter (15.3%) and autumn (14.7%), indicating earlier onset of RSV A circulation. No significant difference was found between sexes (p = 0.196). Conclusions: This study provides the first long-term retrospective analysis of RSV A trends in the Republic of Korea and reveals a shift toward an earlier seasonal onset. These findings support the need for earlier preventive strategies and optimized vaccination timing, particularly for high-risk groups, such as infants. These findings underscore the importance of seasonal variation and the potential influence of environmental factors, such as ambient temperature, relative humidity, and geographic latitude, on RSV A transmission patterns in Korea, although these variables were not directly analyzed in the present study and warrant further investigation.