Seasonal Variation in Respiratory Syncytial Virus Epidemiology Over Nine Consecutive Years of Surveillance

Background Understanding the epidemiological characteristics of respiratory syncytial virus (RSV) prevalence is essential for effective prevention and control measures. Methods An observational study using data from the World Health Organization (WHO) Global Influenza Programme, sourced from Canada, which has completed and long-term records of 5,666,687 RSV surveillance uninterruptedly from the first week of 2016 to the 15th week of 2025. Results Of the 5,666,687 tests, 245,828 were RSV-positive, yielding an overall positivity rate of 4.34%. During nine seasonal years of continuous observation, RSV-positive rate varied year-round, suggesting a feature of seasonality, meaning that RSV epidemics always occurred in winter and spring. The RSV-positive rate also varied year by year in terms of the onset week, offset week, peak week, RSV positivity rate in the peak week, and the number of epidemic weeks. The impact of the COVID-19 pandemic on RSV seasonality in Canada is significant. Most notably, the RSV prevalence in the 2020–2021 season was largely suppressed. Furthermore, in the subsequent three years, variations persisted in the onset week, offset week, peak week, RSV positivity rate in the peak week, and the number of epidemic weeks. Conclusion This report, with a sample size in the millions and covering the pre-, mid-, and post-COVID-19 pandemic periods over nine consecutive years, not only demonstrates the seasonal characteristics of RSV prevalence but also reveals the interaction between the two dominant respiratory viruses.