Transmission-blocking vaccines for respiratory viruses: from concept to clinic

Mucosal vaccines are widely proposed as a way to block respiratory virus transmission more effectively than systemic vaccines, yet supporting clinical evidence remains scarce. This Commentary outlines the obstacles to demonstrating transmission-blocking efficacy, from the absence of standardized correlates of protection to the limitations of animal and trial models, and considers how controlled human infection models, household studies, and field trials could help generate this evidence to support regulatory engagement and licensure.