Change in weight (A, C) and virus titers in the upper respiratory tract (B, D) of vaccinated and control ferrets after challenge with A/JWE/HK/1038/06 (A, B) or A/WS/MG/244/05 (C, D) (H5N1) virus. Ferrets were vaccinated twice (at a 3-week interval) with inactivated whole-virus H5N1 vaccine with MF59 adjuvant and were challenged with 106 EID50 of H5N1 virus one week after the second vaccination. Weight was monitored daily. Each data point represents mean % weight change (A, C) (n=5). The mean SD of all data points in A was ± 3.4%; the mean SD of all data points in C was ± 4.3%. The lower limit of detection of virus in the upper respiratory tract (B, D) was 0.75 log10EID50/mL (dashed line) and for computation purposes values lower than that were not included into calculation of mean virus titers. Results are shown as individual and mean ± SD virus titers in nasal washes. ∞P < 0.05 compared with the unvaccinated control group. Abbreviations: rg-VN - rg-A/VN/1203/04 vaccine; rg-HK – rg-A/HK/213/03 vaccine; rg-JWE – rg-A/JWE/HK/1038/06 vaccine; Multi - multiple-clade vaccine.