Maternal pre-F antibodies of hospitalized respiratory syncytial virus–infected infants in the intensive care unit (ICU) or ward, and maternal antibodies from the control group. Difference between groups calculated by Kruskal–Wallis test followed by Dunn test to adjust for multiple comparisons (ICU vs ward, P > .99; ICU vs controls, P = .28). Abbreviations: ICU, intensive care unit; IgG, immunoglobulin G; NS, not significant; RSV, respiratory syncytial virus.