Assessing treatment efficacy for interval-censored endpoints using multistate semi-Markov models fit to multiple data streams
This study addresses the challenge of estimating treatment effects under multiple interval-censored data. We propose the first semiparametric modeling framework for multistate semi-Markov models and develop a Monte Carlo EM (MCEM) algorithm based on importance sampling to overcome computational bottlenecks arising from high-dimensional, asynchronous observations under coarsening mechanisms. Applied to the REGEN-COV monoclonal antibody clinical trial evaluating household secondary SARS-CoV-2 transmission prevention, our method integrates heterogeneous interval-censored data—including symptom onset, RT-qPCR viral load trajectories, and serological outcomes—to quantify effects on asymptomatic infection risk, viral shedding duration, and seroconversion rate. Results show that REGEN-COV significantly reduces asymptomatic infection risk (HR = 0.32), shortens median viral shedding by 4.1 days, and suppresses seroconversion among asymptomatic individuals. The proposed algorithm achieves 3–5× computational efficiency gains over existing methods, enabling robust modeling of complex real-world interval-censored data.