Nationwide Epidemiology and Outpatient Healthcare Resource Use of Children with Respiratory Syncytial Virus from 2005 to 2021

Background. Respiratory syncytial virus (RSV) poses a global health challenge, particularly among younger children. While the disease burden in Japan has been preliminarily quantified in short-term or inpatient settings, a comprehensive understanding of outpatient settings at a national level is still lacking. Methods. In this retrospective cohort study, we followed 697 802 children until they reached 60 months of age, amounting to 25 680 468 million person-months, using two nationally representative databases from the fiscal years 2005-2021. We analyzed trends in the epidemiology of RSV infections and associated outpatient health resource use. Results. Incidence rates of RSV and associated hospitalizations among infants showed fluctuations of 50-100 cases and 20-30 hospitalizations per 1000 person-years, respectively, during the 2010s. These rates dropped to 8.7 cases and 2.2 hospitalizations per 1000 person-years in 2020, then returned to the same levels in the 2010s. Similar patterns were noted for RSV testing, outpatient visits, healthcare cost, and the proportion of cases hospitalized (case-hospitalization risk). Whereas antibiotic use decreased from 56.4% in 2005 to 27.8% in 2021, palivizumab use increased from 95.2 to 195.9 days of therapy per 1000 person-years. Applying the calculated incidence rates to national data, annual outpatient healthcare costs for RSV infections were estimated to be 7-9 billion JPY (50-64 million USD) for children aged < 60 months in the late 2010s. Conclusions. Our study highlights the changes in epidemiology and outpatient health resource utilization for children with RSV infections. These findings are valuable for policymakers and clinicians aiming to develop strategies, including newly developed maternal vaccines and single-dose long-acting monoclonal antibodies.