Prevalence and Incidence of Respiratory Syncytial Virus and Other Respiratory Viral Infections in Children Aged 6 Months to 10 Years With Influenza-like Illness Enrolled in a Randomized Trial

Respiratory syncytial virus (RSV) is the most important agent to cause acute lower respiratory infection (ALRI) in young children; it also affects older adults and the immunocompromised [1]. RSV infection elicits symptoms ranging from sinusitis and otitis media to bronchiolitis and pneumonia [1]. In temperate climates, outbreaks occur in winter months. Tropical countries also have RSV seasons but with greater variation than in temperate locations [2]. A review of the global burden of RSV estimates an annual incidence of approximately 34 million episodes of ALRI associated with RSV infection in children aged <5 years [3]. Just over 3 million episodes were estimated to result in hospitalization and between 66 000 and 199 000 in death [3]. Most deaths (99%) occur in the developing world [3]. Infants have consistently higher rates of RSV-associated illness and hospitalization than older children in both industrialized and developing nations [3–7]. The high burden of RSV-associated morbidity and mortality means that development of safe and effective vaccines is a priority. Several candidates are in development [8]. However, more information on the epidemiology of RSV is needed to inform control strategies. Few studies have captured RSV burden using community-based active surveillance of healthy children and laboratory-confirmed RSV. In addition, the burden and seasonality of disease in southern hemisphere, tropical, and subtropical countries need to be better understood, as does the burden in specific age groups including older children. Vaccine efficacy trials are ideally placed to evaluate viral epidemiology, as they provide intensive, active follow-up of a well-defined population. As part of an efficacy trial of pandemic influenza vaccines, we evaluated the prevalence and incidence of RSV in children aged 6 months to <10 years at first vaccination and undergoing 1 year of prospective active and passive community-based surveillance for influenza-like illness (ILI).