RSV F-specific serum and lung antibody titers in vaccinated young and aged BALB/c mice. Day 27 serum was examined by ELISA for (A) RSV F-binding IgG and (B) RSV F-binding IgG2a or IgG1 subtype antibodies using isotype-specific anti-mouse detection antibodies. (C) Lung homogenates 4 days post-challenge were examined for RSV F-binding IgG antibodies. The dotted line represents the lower limit of detection (LLOD= 1:50 dilution). ***, P < 0.0001 comparing F + alum to placebo in young mice (ANOVA). *, P < 0.05 comparing F + alum to F in young mice (ANOVA). ###, P < 0.0001 comparing F + alum to placebo or F in aged mice (ANOVA). Serology results were combined from two independent experiments.