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Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in young children. We previously estimated that in 2015, 33·1 million episodes of RSV-associated acute lower respiratory infection occurred in children aged 0–60 months, resulting in a total of 118 200 deaths worldwide. Since then, several community surveillance studies have been done to obtain a more precise estimation of RSV associated community deaths. We aimed to update RSV-associated acute lower respiratory infection morbidity and mortality at global, regional, and national levels in children aged 0–60 months for 2019, with focus on overall mortality and narrower infant age groups that are targeted by RSV prophylactics in development.

BackgroundEarly recognition of children at risk of severe respiratory syncytial virus (RSV) lower respiratory tract infection is important as it informs management decisions. We aimed to evaluate factors associated with severe disease among young children hospitalised with RSV infection.MethodsWe conducted a retrospective cohort study of all children <2 years of age hospitalised for RSV lower respiratory tract infection at a single tertiary paediatric hospital over three RSV seasons (January 2017–December 2019). We classified children as having ‘moderate’ or ‘severe’ disease based on the level of respiratory intervention and used univariable and multivariable regression models to determine factors associated with severe disease.ResultsOf 970 hospitalised children, 386 (40%) were classified as having ‘severe’ and 584 (60%) as having ‘moderate’ RSV disease. On multivariable analyses, age <2 months (OR: 2.3, 95% CI 1.6 to 3.3, p<0.0001), prematurity (OR: 1.6, 95% CI 1.1 to 2.4, p=0.02) and RSV–parainfluenza virus type 3 (PIV3) codetection (OR: 2.6, 95% CI 1.05 to 6.5, p=0.04) were independently associated with severe disease.ConclusionYounger age, prematurity and PIV3 codetection were associated with severe RSV disease in children <2 years of age hospitalised with RSV infection. The association between PIV3 and severe RSV disease is a novel finding and warrants further investigation.

Respiratory syncytial virus (RSV) is the most common viral pathogen associated with acute lower respiratory tract infection (LRTI) in children under 5 years of age. Severe RSV disease is associated with the development of chronic respiratory complications such as recurrent wheezing and asthma. A common risk factor for developing severe RSV disease is premature gestation and this is largely due to an immature innate immune system. This increases susceptibility to RSV since the innate immune system is less able to protect against pathogens at a time when adaptive immunity has not fully developed. This review focuses on comparing different aspects of innate immunity between preterm and term infants to better understand why preterm infants are more susceptible to severe RSV disease. Identifying early life innate immune biomarkers associated with the development of severe RSV disease, and understanding how these compare between preterm and term infants, remains a critically important question that would aid the development of interventions to reduce the burden of disease in this vulnerable population.