Influenza virus challenge. At week 5, mock vaccinated mice or mice vaccinated with vaccines were challenged intranasally with reassortant H5/PR8 influenza viruses representing (A) VN/04 or (B) Indo/05. Mice were monitored daily for weight loss, activity, and survival. Body weight is plotted as percentage of the average initial weight. Mice that lost greater than 30% body weight were sacrificed.