Aims and objectives: Respiratory syncytial virus (RSV) incidence is underestimated, due to nonspecific symptomatology and infrequent testing, particularly among adults. We aimed to estimate population-based incidence of RSV-attributable hospitalizations and deaths in Spain using a retrospective statistical model-based approach.

Methods:  We obtained national hospital discharge (2016?2019) and mortality (2015?2019) data. We estimated RSV-attributable incidence of respiratory hospitalizations and deaths (total and stratified by age and disease subgroups) using a quasi-Poisson regression model that accounted for baseline seasonal variation throughout the year and incorporated hospitalizations for RSV in children <2 years and influenza in adults ?60 years as viral circulation proxies.

Results: The estimated RSV-attributable incidence rate of respiratory hospitalizations increased gradually from 2016?2019. In children <1 year, it increased from 2,667 to 3,735 (0-5 months of age: 4,081 to 5,715; and 6-11 months: 1,252 to 1,754) cases per 100,000 person-years. In adults aged ?60 years, incidence increased from 268 to 307 (7 to 8, 21 to 22, 130 to 147 and 686 to 822 in 18?49, 50?59, 60?79 and ?80 age groups, respectively) cases per 100,000 person-years. Mortality data will be presented at the congress.

Conclusions: These model-based RSV hospitalization incidence estimates were comparable to a global meta-analysis assessing adults ?65 years (157?347/100,000 Li et al) and a UK study assessing children <6 months (4,184/100,000 Taylor et al). When accounting for underdiagnosis, RSV causes a considerable burden of hospitalizations, suggesting an efficacious vaccine could have a high public health impact.