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Background: The fusion (F) glycoprotein of respiratory syncytial virus (RSV) represents the major neutralizing antigen, and antibodies against the pre-F conformation have the most potent neutralizing activity. This study aimed to assess the correlation between maternal antibody titers against the pre-F, post-F, and G glycoproteins and the child's risk of developing severe RSV bronchiolitis early in infancy.Methods: We identified previously healthy term infants <3 months of age hospitalized with RSV bronchiolitis from December 2015 to March 2016. We measured IgG antibody titers to pre-F, post-F, and G proteins in maternal sera obtained at 9-12 weeks of pregnancy of these hospitalized infants' mothers (n = 94) and compared them with serum antibody titers of control pregnant mothers (n = 130) whose children were not hospitalized.Results: All maternal samples (n = 224) had detectable pre-F antibodies. Pre-F antibody titers were significantly lower in mothers whose infants were hospitalized with RSV bronchiolitis compared with those mothers whose infants were not hospitalized (23.9 [range (or antibody titer range), 1.4-273.7] µg/L vs 30.6 [XXX, 3.4-220.0] µg/L; P = .0026). There were no significant differences in maternal post-F and G antibody titers between hospitalized and nonhospitalized infants.Conclusions: Our findings indicate that maternal pre-F antibodies are fundamental for providing immune protection to the infant. [ABSTRACT FROM AUTHOR]