Efficient host transmission of measles virus: disentangling misconceptions from established findings.

SUMMARYMeasles virus (MeV) is considered the most contagious human virus. This review critically examines explanations for MeV's extraordinary transmissibility. Although substantial progress has been made in understanding MeV infection, pathogenesis, and host spread, the fundamental question of why MeV is markedly more transmissible than other structurally similar respiratory viruses within the same taxonomic families remains unresolved. Many commonly cited explanations are either incorrect, oversimplified, or insufficiently supported by rigorous experimental evidence. Notably, there is a striking lack of studies that directly investigate the mechanisms governing MeV transmission. This knowledge gap persists in part because humans are the only natural reservoir for MeV, and thus the most relevant experimental models can be costly, technically challenging, and limited in ability. Moreover, studies addressing MeV environmental stability have relied largely on in vitro laboratory conditions that may have limited relevance to real-world transmission scenarios. While these studies have yielded useful observations, they often lack definitive mechanistic insight into efficient host-to-host spread. In this review, we discuss multiple strategies to investigate and define the efficient transmission of MeV, including (i) epidemiology, (ii) stability in controlled environments, (iii) infectious dose, (iv) incubation period, and (v) shedding from the respiratory epithelium. As will be discussed, quantitative, head-to-head comparisons of MeV transmission dynamics with those of other common respiratory viruses, such as influenza virus, rhinovirus, and respiratory syncytial virus, are notably absent. A clearer understanding of the mechanisms that govern efficient MeV transmission may inform strategies to reduce spread in educational, healthcare, and community settings.