[The design of emulated target trials and the application in evaluating vaccine effectiveness]

Randomized controlled trials have long been regarded as the gold standard for evaluating vaccine efficacy. However, conducting randomized controlled trials to assess vaccines in real-world settings is often impractical due to limitations in research resources and ethical considerations. In recent years, the emulated target trial has emerged as a novel methodological framework that applies the design principles of randomized trials to observational studies. By using observational data to emulate the randomization and treatment assignment of a clinical trial, this approach enables the evaluation of vaccine effectiveness in the real world. The application of emulated target trials enhances the quality and applicability of real-world evidence. This article explains the fundamental principles, design elements, advantages, and limitations of using emulated target trials to evaluate vaccine effectiveness, providing methodological guidance for conducting such studies in China.