Respiratory viral coinfections: interactions, mechanisms and clinical implications

Many heterologous viruses that infect the respiratory tract co-circulate within human populations. With the advent of multiplex diagnostic tests for respiratory viruses, there is increased appreciation of viral coinfection within an individual host. Thus, it is important to understand the interactions between heterologous respiratory viruses at the levels of populations, hosts and cells, as well as the impact of these interactions on pathogen prevalence and disease severity. In this Review, we summarize studies that demonstrate antagonistic or synergistic interactions between respiratory viruses, resulting in altered viral prevalence in populations, replication in hosts and cells, and disease severity in clinical cases and animal models. Understanding these interactions at a mechanistic level will affect future strategies to prevent and treat respiratory viral infections.