Cost-effectiveness of casirivimab/imdevimab in patients with COVID-19 in the ambulatory setting

BACKGROUND: Most patients infected with SARS-CoV-2, resulting in COVID-19, have only mild symptoms that can be managed in an ambulatory setting. However. a significant number of patients develop a more severe form of the disease and require hospital care, with the risk of long-term sequetae or death. Casirivimab/imdevimab is a combination of 2 recombinant human monoclonal antibodies that has been shown to significantly reduce the risk of hospitalization or death in patients with mild to moderate COVID-19 in the ambulatory setting. OBJECTIVE: To establish the cost-effectiveness of casirivimab/imdevimab in ambulatory individuals with COVID-19. METHODS: A cost-effectiveness model was constructed to simulate the natural history of COVID-19 in ambulatory patients and to identify those patients for whom casirivimab/imdevimab may be a cost-effective treatment from a US payer perspective. Patients enter the model in the ambulatory health state and can receive either active treatment with casirivimab/imdevimab or usual care. Patients can either recover from the infection or be hospitalized, from where they can recover from infection or die. Following this acute phase, patients enter a Markov model to estimate lifetime quality-adjusted life years. The model uses the risk of hospitalization in both the active treatment and usual care cohorts, and age- and sex-specific risk of mortality. Other model inputs include hospitalization costs and health-related utilities in the ambulatory acute treatment phase, the hospitalized setting, and the post-acute phase. Accounting for the heterogeneity of risk by age and comorbidities, results are presented separately for various combinations of baseline age and usual care risk in a 7x9 matrix. Outcomes related to "long COVID" are assessed in scenario analyses. RESULTS: In the base case, at a willingnessto-pay threshold of $100,000. treatment with casirivimab/imdevimab was found to be costeffective in most patients, including those older than 40 years of age with a baseline hospitalization risk greater than or equal to 2% and patients aged 20 years with a baseline risk of hospitalization greater than or equal to 4%, whereas for hospitalization risk greater than or equal to 10%, casirivimab/imdevimab is dominant. Casirivimab/imdevimab was not cost-effective in patients aged 20 years with a 3% or tower risk of hospitalization or in patients aged 30 years with a 2% risk. CONCLUSIONS: This economic analysis found that casirivimab/imdevimab is a cost-effective treatment for most ambulatory patients with COVID-19.