OBJECTIVES: Respiratory syncytial virus (RSV) is the leading cause of viral lower respiratory tract illness (LRTI) in young children and is associated with significant morbidity, especially among infants. Nirsevimab is a monoclonal antibody being developed as a passive immunization for the prevention of medically attended RSV-LRTI (RSV MALRTI). Understanding its health economic impact under different scenarios is important to determine the optimal implementation strategy to protect all infants entering their first RSV season. The objective of this work was to explore the impact of nirsevimab in a UK birth cohort compared to current standard of practice and identify the most impactful approaches to implementation.

METHODS: A static Markov model was developed to estimate RSV MALRTIs and costs in a UK birth cohort over their first RSV season (October to March). A cycle length of one month was employed to expose the cohort to differential risk of RSV according to age in months at start of the season and circulating seasonal RSV density.

RESULTS: Under current standard of practice, the model estimated 149,260 [147,603 – 152,295] RSV MALRTIs over one season with an associated annual economic burden estimated at £95 million [£92M – £100M]. RSV related hospitalizations were almost equally distributed between infants born within season (WiS) and infants born out of season (OoS) with 45% & 55% respectively. Forty-one percent of all RSV MALRTIs were found among WiS births and 59% within OoS births. The most impactful approach was to immunize all infants (WiS & OoS), with more than 65% reduction of cases when a coverage rate of 85% and an efficacy of 70% was assumed with a 5-month window of protection.

CONCLUSIONS: Nirsevimab is likely to represent value for money if used on a seasonal basis targeted towards protecting all infants during the first year of life within their first RSV season.