Anderson J, Oeum M, Verkolf E, et al. - According to this retrospective cohort study, younger age, prematurity and parainfluenza virus type 3 (PIV3) codetection were associated with severe respiratory syncytial virus (RSV) disease in children < 2 years of age hospitalized with RSV infection. The link between PIV3 and severe RSV disease is a unique discovery that merits further exploration.

• From January 2017 to December 2019, children < 2 years of age hospitalized for RSV lower respiratory tract infection at a single tertiary paediatric hospital over three RSV seasons were analyzed.

• Of the 970 hospitalized children, 386 (40%) were diagnosed as having ‘severe' RSV disease, while 584 (60%) were classed as having ‘moderate' RSV disease.

• Age < 2 months, prematurity and RSV–PIV3 codetection were all independently related to severe disease in multivariable analysis.