FIG. 4.

Replication of H7 wt challenge viruses in the respiratory tract of ferrets immunized with the H7N7 NL/03 ca virus. Groups of ferrets were immunized with 1 dose (□) or 2 doses (⋄) of 10⁷ TCID₅₀/ferret of the H7N7 NL/03 ca virus or were mock immunized (L-15) (•), and four ferrets per group were challenged 4 weeks after doses 1 and 2 with 10⁶ TCID₅₀/ferret of each indicated virus. Nasal turbinates (A) and lungs (B) were harvested 3 days following challenge, homogenized, and titrated on MDCK cells and embryonated eggs, respectively. Virus titers are expressed as log₁₀ TCID₅₀/g or log₁₀ EID₅₀/g of tissue. The solid line represents the mean for the group. The lower limit of detection is indicated by the dashed horizontal line. An asterisk indicates a statistically significant (P < 0.05) reduction in virus titers compared to the titers in the mock-immunized group.