OBJECTIVES: Respiratory syncytial virus (RSV) is the leading cause of hospitalization in all infants in North America. Nirsevimab, an anti-prefusion F RSV monoclonal antibody with an extended half-life administered to infants, and the maternal vaccine (MV) RSVpreF, a bivalent RSV prefusion F protein–based administered during pregnancy. The aim of this study was to estimate the protection offered by each product in terms of number of events avoided during the first RSV season of infants’ life, compared to standard of practice, in the US.

METHODS: We used a static model to analyze the impact of new interventions for the prevention of RSV lower respiratory tract disease (LRTD) in the US birth cohort. The efficacy of nirsevimab is sourced from MEDLEY, Ph2b, MELODY and HARMONIE trials. The efficacy of MV is based on MATISSE results.

RESULTS: A total of 291,320 events could be prevented with nirsevimab, while MV, with the same coverage rate (80%), would prevent about half as many events (144,278). The differential (figure 1) can be attributed to the following features of nirsevimab, lacking for MV: (i) the constant efficacy over time versus decay of maternal protection, (ii) a timely immunization when RSV circulates, (iii) the protection of all infants regardless of gestational age, (iv) the significant protection against all-cause LRTD hospitalizations. Additionally, we performed a sensitivity analysis assuming that RSVpreF will be ranked in fourth position, after influenza, Tdap and COVID immunizations in pregnant women resulting in a lower coverage rate (50%) and fewer number of events averted with MV (90,174 – 69% less than nirsevimab).

CONCLUSIONS: Nirsevimab is estimated to prevent more cases than MV due to unique features of maintained efficacy through a typical RSV season, timely immunization, ability to protect regardless of the gestational age, and significant protection against all-cause LRTDs.