Fig 4.

Cross-protection of mice against the homotype, a drift variant within the subtype, or different subtypes of an influenza virus strain by intranasal immunization with A/PR/8/34 WV vaccine and its SV vaccine plus poly(I·C). Groups of mice (5 per group) were inoculated twice intranasally with PBS, 10 μg of poly(I·C), a mixture of 1 μg of A/PR/8/34 SV vaccine and 10 μg of poly(I·C) [SV+poly(I·C)], or 1 μg of A/PR/8/34 WV vaccine (WV). Fourteen days after the final immunization, the mice were infected with A/PR/8/34 (H1N1; 10³ PFU) (A), A/Brisbane/59/2007 (H1N1; 10⁷ PFU) (B), or A/Hiroshima/53/2005 (H3N2; 10⁷ PFU) (C), and the mortality was assessed. *, P < 0.05 versus the group inoculated intranasally with PBS.