In-Use Stability and Functional Efficacy of a Monoclonal Antibody Cocktail (TwinRab™) for Rabies Post-exposure Prophylaxis

Rabies remains a major public health problem in India, accounting for nearly one-third of global human deaths each year. Limited access to human and equine rabies immunoglobulins (RIGs) continues to restrict effective post-exposure prophylaxis (PEP) coverage, particularly in resource-limited settings. TwinRab™, a two-antibody monoclonal cocktail containing docaravimab and miromavimab, was developed as a standardized, scalable alternative to plasma-derived RIGs. This study evaluated the in-use stability and biological efficacy of TwinRab™ under simulated field-use conditions. In the in vitro arm, TwinRab™ samples from 300 IU/mL and 600 IU/mL batches were diluted in 0.9% sodium chloride to obtain twofold, fivefold, and 10-fold dilutions and stored at room temperature (25 ± 2 °C) for 4-24 hours. Potency was measured using the rapid fluorescent focus inhibition test (RFFIT) against the CVS-11 rabies virus strain. In the in vivo arm, undiluted TwinRab™ was administered six or 24 hours after viral challenge in a Syrian hamster model, and survival outcomes were compared with human RIG (Kamrab). TwinRab™ retained its neutralizing potency after dilution and ambient storage for up to 24 hours. The 600 IU/mL batch showed no significant loss of activity across all dilutions (p > 0.05), while minor but statistically significant differences were noted at higher dilutions of the 300 IU/mL batch (p < 0.05). In vivo, TwinRab™ achieved 90% survival when administered six hours post-challenge and 70% when administered after 24 hours, demonstrating comparable efficacy to Kamrab. These findings confirm that TwinRab™ maintains stability and functional efficacy under conditions that simulate routine clinical practice. Its thermostability, potency, and protective efficacy highlight its potential as a field-adaptable, next-generation alternative to conventional RIGs for PEP, particularly in high-burden regions with limited cold-chain infrastructure.