Palivizumab and ribavirin reduce infectious virus in mouse lungs, but only ribavirin affects intracellular viral replication. Naïve Balb/c mice and mice treated prophylactically with 5 mg/kg palivizumab were infected intra nasally with 2.3 × 106 FFU RSV A2. A third group were treated with ribavirin prior to RSV administration and throughout the study period as described in materials and methods. A) Negative and B) positive sense strand RSV RNAs were quantified by strand-specific QPCR. Means ± SEM for 6 animals per time point are plotted. Normalised RSV copy number was determined from strand-specific RNA standard curves corrected by beta actin arbitrary copy number. C) A ratio index of positive to negative strand RNA was constructed and time course profiles for ribavirin and palivizumab treatments are plotted against untreated RSV infected values. Means ± 95% confidence intervals (n = 6) are shown. D) Infectious live virus in mouse lungs was monitored by FFU assay throughout the time-course. Means ± SEM (n = 6) are plotted. Asterisks indicate significant difference (p ≤ 0.05) to untreated RSV-infected values at each sampling time. No data was collected post day 7 and is depicted as ND on the graph.