Clinical efficacy of casirivimab and imdevimab in preventing COVID-19 in the Omicron BA.5 subvariant epidemic: a retrospective study

Background: The neutralizing monoclonal antibody combination of casirivimab and imdevimab (CAS + IMD) is the only therapy approved for preventing coronavirus disease 2019 (COVID-19) following exposure to severe acute respiratory syndrome coronavirus 2. However, the efficacy of CAS + IMD against Omicron variants remains uncertain, with in vitro studies indicating reduced neutralizing activity. This study aimed to evaluate the clinical efficacy of CAS + IMD in preventing COVID-19 among uninfected hospitalized contacts of patients with COVID-19. Methods: A retrospective chart review was conducted on 154 inpatients exposed to patients with COVID-19 between October and December 2022. Fifty-two uninfected participants who were unvaccinated or immunosuppressed and had risk factors for severe COVID-19 were included. The primary endpoint was the COVID-19 incidence rate. Statistical analyses included the chi-square test, Fisher's exact test, and Mann–Whitney U test, as appropriate. Factors associated with COVID-19 incidence ( p < 0.02) in univariate analysis were included in the multivariate logistic regression. Statistical significance was set at p < 0.05. Results: Among the 52 participants, 14 and 38 were included in the CAS + IMD and non-CAS + IMD groups, respectively. The COVID-19 incidence rate was significantly lower in the CAS + IMD group than in the non-CAS + IMD group (14.3% vs. 52.6%, p = 0.013). Multivariate analysis identified CAS + IMD administration as significantly associated with reduced COVID-19 incidence (adjusted odds ratio [OR], 0.121; 95% confidence interval [CI], 0.020–0.710; p = 0.019), whereas long-term use of immunosuppressive therapy was associated with increased incidence (adjusted OR, 4.320; 95% CI, 1.090–17.126; p = 0.037). Conclusions: CAS + IMD may be effective for post-exposure prophylaxis of COVID-19 during the Omicron BA.5 subvariant epidemic. However, prudent clinical use should consider the circulating variant profile. Further research is warranted to validate CAS + IMD’s role in COVID-19 post-exposure prophylaxis.