Figure 1. Neonatal nasal vaccination with N+LT conferred viral protection but exacerbated airway disease upon RSV challenge.

Male and female pups (5–7 day-old) were vaccinated by intranasal instillation of 10 µL saline containing or not 3 µg N and 2 µg LT as indicated. At 5 weeks of age, mice were challenged by intranasal instillation of 50 µL (5.10⁶ pfu) hRSV A2. Controls included unvaccinated infected (C+) and uninfected (C−) littermates. Animals were killed 5 days post challenge (d5 p.i.). (A) Individual viral load assessed by qRT-PCR: R.Q. of N transcripts, normalized to HPRT, are expressed as % of the unvaccinated infected control group (C+) (R.Q. = 100×2^−ΔΔCt). Four independent experiments combining different treatment groups are shown with ≥5 mice per group (C−: n = 7, C+: n = 10, LT: n = 5, N: n = 16, N+LT: n = 20). Mann-Whitney U-test was used for comparison between treatments (* p<0.05; *** p<0.001 and **** p<0.0001). (B) Mice were weighed daily from d0 till d5 p.i. and individual weight loss/gain was calculated as % of initial weight. Data are mean±SEM from n≥5 mice per group. Statistical analysis was performed to compare growth over the period d2 to 5 p.i. using the Tukey's multiple comparison test, repeated measures one way ANOVA (** p<0.01 and *** p<0.001).