key: cord-0915191-0ig6ohhz authors: Foley, David A; Yeoh, Daniel K; Minney-Smith, Cara A; Martin, Andrew C; Mace, Ariel O; Sikazwe, Chisha T; Le, Huong; Levy, Avram; Moore, Hannah C; Blyth, Christopher C title: The Interseasonal Resurgence of Respiratory Syncytial Virus in Australian Children Following the Reduction of Coronavirus Disease 2019–Related Public Health Measures date: 2021-02-17 journal: Clin Infect Dis DOI: 10.1093/cid/ciaa1906 sha: 9cc7715c187eb4884455c4e390ff78d84215d105 doc_id: 915191 cord_uid: 0ig6ohhz nan To the Editor-Yeoh et al reported the dramatic impact of public health measures introduced during the coronavirus disease 2019 (COVID-19) pandemic on influenza and respiratory syncytial virus (RSV) detections in Western Australian (WA) children [1] . Here, we present data from ongoing local prospective surveillance. Following the end of winter, there has been a persistent absence of severe acute respiratory syndrome coronavirus 2 community transmission and no increase in influenza detections. Limited physical distancing measures have remained in place, with largely no restrictions on gathering sizes and no mandate for wearing masks [2] . Schools have remained open. Strict quarantine for overseas arrivals has been maintained, with a persistent marked decrease in visitor numbers compared with previous numbers [3] . Border restrictions for travelers from other states within Australia have been reduced as of 14 November 2020, with quarantine not required for travelers from states with no community severe acute respiratory syndrome coronavirus 2 transmission [4] . Similar to the previous report laboratory data prospectively collected as part of routine regional public health surveillance were collated per week from January 2012 to 13 December 2020. Cases were defined as detections of RSV by validated nucleic acid amplification test or antigen detection kits in children (<16 years of age) in the metropolitan area. Laboratory results were provided by PathWest Laboratory Medicine, the only public pathology provider to the state. Samples were drawn from all public hospitals and emergency departments. Average epidemic curves for the period 2012 to 2019 were calculated using a World Health Organization-described method [5] . Median age was compared using 2-sample Wilcoxon test. As demonstrated in Figure 1 , RSV activity increased from late September, in the setting of relaxed physical distancing recommendations, ahead of the opening of interstate borders. Case numbers have further increased, exceeding the median seasonal peak from 2012 to 2019. This has been observed without any significant change in testing practices. The median patient age this year was 18.4 months, significantly higher than the upper range between 2012 and 2019 (7.3-12.5 months) (P < .001). These data demonstrate the fragility of RSV control and the critical impact of physical distancing and respiratory hygiene practices. The rise in numbers and change in median age suggest that the expanded cohort of RSV-naïve patients, including an increased number of older children coupled with waning population immunity [6] , may have contributed to this marked resurgence. Notably, RSV activity was first observed in mid-late August in regional centers before emergence in the metropolitan area, with transmission potentially facilitated by increased travel within the state [7] . Conversely, the initial rise in RSV cases in WA preceded the opening of interstate borders, suggesting this pathway was not the primary mechanism. Our findings raise concerns for RSV control in the Northern Hemisphere, where a shortened season was experienced last winter [8] . The eventual reduction of COVID-19-related public health measures may herald a significant rise in RSV [9] . Depending on the timing, the accompanying morbidity and mortality, especially in older adults [6] , may overburden already strained healthcare systems. To delineate the relative contribution of an increasingly susceptible population and the reduction in border restrictions, further surveillance, transmission studies, and assessment of relatedness of RSV strains is progressing. Financial support. This was an investigatorinitiated project supported by a clinician-scientist partnership grant from the Wesfarmers Centre for Vaccines and Infectious Diseases (2020 The impact of COVID-19 public health measures on detections of influenza and respiratory syncytial virus in children during the 2020 Australian winter COVID-19 coronavirus: WA roadmap Overseas arrivals and departures Australia 2020 Covid 19 Coronavirus: what you can and can't do 2020 World Health Organization. Global epidemiological surveillance standards for influenza Immunity to RSV in early-life Mobility trend reports 2020 Effect of social distancing due to the COVID-19 pandemic on the incidence of viral respiratory tract infections in children in finland during early 2020 The impact of COVID-19 nonpharmaceutical interventions on the future dynamics of endemic infections