Epidemiology of Respiratory Syncytial Virus Across Five Influenza Seasons Among Adults and Children One Year of Age and Older-Washington State, 2011/2012-2015/2016

Background. Vaccines and novel prophylactics against respiratory syncytial virus (RSV) are in development. To provide a baseline for evaluating these interventions, we characterized the incidence and molecular epidemiology of RSV in persons aged >= 1 year. Methods. We identified patients with medically attended acute respiratory illness (MAARI) from the 2011/2012 through 2015/2016 influenza seasons among members of Kaiser Permanente Washington. We estimated the cumulative incidence of MAARI for laboratory-confirmed RSV or influenza infection. Results. Annual cohorts ranged from 82 266 to 162 633 individuals, 14% of whom were children aged 1 to 17 years. Cumulative incidence of RSV each season ranged from 14 per 1000 population (95% confidence interval [CI], 12-16) to 22 per 1000 (95% CI, 19-25). Incidence of RSV was greater than influenza in children aged 12-23 months and 2-4 years; incidence of influenza was greater in other age groups. Respiratory syncytial virus subtype A dominated in 2011/2012, 2012/2013, and 2015/2016, with ON1 being the most common genotype. Respiratory syncytial virus subtype B dominated in 2013/2014 and 2014/2015, primarily of the BA genotype. Conclusions. The burden of RSV is comparable to that of influenza across the life course. These results provide a baseline for evaluating the impact of new RSV interventions on the epidemiology of RSV.