Fig 6.

Vaccination of mice with NS1-truncated viruses encoding a “superpromoter” in the HA segment confers enhanced serum anti-influenza virus titers and improved survival following challenge. Mice (5 per group) were vaccinated with 10 PFU or 100 PFU of either the PR8 NS1 1-73 virus (73) or the PR8 NS1 1-73 virus encoding the G3A C8U mutations in the HA segment (S73). Positive-control mice were vaccinated with 10 PFU of the wild-type PR8 virus. Negative-control mice were immunized with PBS. Three weeks postvaccination, mice were bled; then they were challenged with 100 MLD₅₀s of the wild-type PR8 virus. (A) Serum anti-influenza virus antibody titers 3 weeks postvaccination. Shown is the average titer (with the standard error) for 5 mice per group at a 1/800 dilution of the sera. OD, optical density. (B and C) Survival curves of mice vaccinated with 100 PFU (B) or 10 PFU (C) of the indicated viruses and challenged with 100 MLD₅₀s of wild-type PR8 virus 3 weeks postimmunization.