A Health Economic Evaluation for Implementing an Extended Half-life Monoclonal Antibody for All Infants vs. Standard Care for Respiratory Syncytial Virus Prophylaxis in Canada

Respiratory syncytial virus (RSV) is a highly infectious virus, and infants and young children are particularly vulnerable to its progression to severe lower respiratory tract illness (LRTI). Nirsevimab, an extended half-life monoclonal antibody, was recently approved in Canada as a passive immunization intervention for the prevention of RSV LRTI. A static decision tree model was utilized to determine the cost-effectiveness of nirsevimab in Canadian infants compared to current standard of care (palivizumab for infants born preterm, and with specific chronic conditions) and generate an optimal price per dose (PPD) at accepted willingness-to-pay (WTP) thresholds. Various health outcomes (including hospitalization, ICU, and mechanical ventilation) and healthcare costs were calculated over one RSV season, with any necessary follow-up prophylaxis in the second season for three infant categories (palivizumab-eligible, preterm, and term). All health-related parameters and costs were tailored to the Canadian environment. Compared to scenarios where only at-risk segments of the infant population received nirsevimab, the base case (administering nirsevimab to all infants in their first RSV season) was the most cost-effective versus standard care: the PPD was $692 at a $40,000/QALY WTP threshold, using average costing data assumptions across all scenarios. Compared to standard care, the base case scenario could avoid 18,249 RSV-related health outcomes (reduction of 9.96%). Variations in discount rate, distribution of monthly RSV infections, nirsevimab coverage rate for infants born at term, and palivizumab cost had the most significant model impact. Passive immunization of all infants with nirsevimab can significantly reduce RSV-related health and economic burden across Canada. ### Competing Interest Statement TS, JKHL, MG and AK are employees of Sanofi, the manufacturer of nirsevimab (jointly with AstraZeneca). JW currently serves as the Sanofi Industrial Research Chair. ### Funding Statement This work was supported by Sanofi and AstraZeneca. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Please contact the primary author for any inquiries pertaining to the model and input data.