Background Influenza and respiratory syncytial virus (RSV) are associated with substantial morbidity and mortality in the United States. We assessed risk factors for severe disease and medical resource utilization (MRU) among US adults hospitalized with influenza or RSV in the Hospitalized Acute Respiratory Tract Infection (HARTI) study. Methods HARTI was a prospective global (40 centers, 12 countries) epidemiological study of adults hospitalized with acute respiratory tract infections conducted across the 2017–2019 epidemic seasons. Patients with confirmed influenza or RSV were followed up to 3 months post‐discharge. Baseline characteristics, prevalence of core risk factors (CRFs) for severe disease (age ≥65 years, chronic heart or renal disease, chronic obstructive pulmonary disease, or asthma), and MRU were summarized descriptively. Results The US cohort included 280 influenza‐positive and 120 RSV‐positive patients. RSV patients were older (mean: 63.1 vs. 59.7 years) and a higher proportion had CRFs (87.5% vs. 81.4%). Among those with CRFs (influenza, n = 153; RSV, n = 99), RSV patients required longer hospitalizations (median length of stay: 4.5 days) and a greater proportion (79.8%) required oxygen supplementation during hospitalization compared with influenza patients (4.0 days and 59.5%, respectively). At 3 months post‐discharge, a greater proportion of RSV patients with CRFs reported use of antibiotics, antitussives, bronchodilators, and inhaled and systemic steroids versus those with influenza and CRFs. Many patients with CRFs reported hospital readmission at 3 months post‐discharge (RSV: 13.4%; influenza: 11.9%). Conclusions MRU during and post‐hospitalization due to RSV in adults is similar to or greater than that of influenza. Enhanced RSV surveillance and preventive and therapeutic interventions are needed.

Background Respiratory syncytial virus (RSV) is shown to cause substantial morbidity, hospitalization, and mortality in infants and older adults. Population-level modelling of RSV would allow for estimation of the full burden of disease and the potential epidemiological impact of novel prophylactics. Methods We model the epidemiology of RSV in the US across all ages using a deterministic compartmental transmission model. Population-level symptomatic RSV acute respiratory tract infection (ARI) cases were projected across different natural history scenarios, both with and without vaccination of older adults aged ≥ 60. Impact of vaccine efficacy against ARIs and infectiousness and vaccine coverage on ARI incidence were assessed. Impact on medical attendance, hospitalization, complications, death and other outcomes were also derived. Results In the absence of a vaccine, we project 17.5-22.6 million symptomatic RSV ARI cases per year in ≥18-year-olds in the US, with 3.6-4.8 million/year occurring in ≥60-year-olds. Modelling indicates that up to 2.0 million symptomatic RSV ARI cases per year could be prevented in ≥60-year-olds with a hypothetical vaccine (70% vaccine efficacy against symptomatic ARI, and 60% vaccine coverage), and up to 0.69 million cases per year can be prevented in the non-vaccinated population, assuming 50% vaccine impact on infectiousness. Conclusions The model provides estimated burden of RSV in the US across all age groups, with substantial burden projected specifically in older adults. Vaccination of ≥ 60 years-old population could significantly reduce the burden of disease in this population, with additional indirect effect in the < 60 years-old population due to reduced transmissibility.