2557. A Model to Estimate the Potential Impact of Immunizations on Respiratory Syncytial Virus (RSV) Disease Burden Among Infants in the United States

BACKGROUND: Respiratory syncytial virus (RSV) is the leading cause of severe respiratory infections among infants worldwide. We developed a mathematical model to estimate the impact of immunizations currently under development on medically attended (MA) RSV infections (RSVi) among infants in the United States. METHODS: We created a spreadsheet-based Decision Tree model to estimate the potential impact of (1) a vaccine given to mothers in their third trimester to indirectly provide protective antibodies to infants during their first RSV season and (2) a monoclonal antibody given to infants at birth during the RSV season (November to April). We measured the annual number of MA-RSVi (hospitalizations, emergency department (ED) visits, and outpatient clinic visits) prevented by immunization before infants reach 6 months of age. Major inputs included population-based rates (from 2000 to 2009) of MA-RSVi in each healthcare setting, immunization uptake, time required to reach partial or full protection, efficacy, and duration of protection. We used 95% confidence intervals of MA-RSVi rates to generate a range of impact estimates. RESULTS: At baseline (without intervention), we estimated 54,523 RSV-associated hospitalizations (range 45,129–64,148), 141,646 ED visits (range 117,358–166,132) and 410,205 outpatient clinic visits (range 339,535–480,681) occur among infants <6 months of age. We used these baseline estimates, an efficacy of 79% for both products, uptake of 60% for the maternal vaccine (based on uptake of maternal tetanus/diphtheria/pertussis vaccine) or 70% for the monoclonal antibody (based on uptake of hepatitis B vaccine birth dose) and assumed a duration of protection of infants between 3 and 5 months to assess immunization impact. With the immunization strategies analyzed, we estimated between 14,591 and 30,336 hospitalizations, 20,621 and 79,020 ED visits, and 58,670 and 228,840 outpatient visits associated with RSVi could be prevented each year. CONCLUSION: Immunization products under development have the potential to substantially reduce MA-RSVi. This model will be used to assess the benefits of different immunization strategies developed to protect infants against RSVi. The model is flexible and can be updated as more data become available. DISCLOSURES: All authors: No reported disclosures.