FIG. 1.

Viruses with different HAs differ in virulence based on their level of glycosylation. Groups of 6 mice were infected with 1 × 10⁶ EID₅₀ of reassortant viruses expressing the HA from HK68 (7 glycosylation sites), Len86 (9 sites), or Pan99 (12 sites) paired with the NA from HK68 (A and B) or Syd97 (C and D) to determine the effect of glycosylation on morbidity (weight loss) (A and C) and survival (B and D). An asterisk denotes a statistically significant difference compared to the group infected with a virus expressing the Pan99 HA; a double asterisk indicates a significant difference compared to both other viruses.