Figure 2.

Antiviral efficacy of FluLaval 2016–2017 in the young and aged cotton rats when given as a two-times (a) vs. one-time (b) immunization. (a) Two-times vaccination. Young and aged cotton rats were immunized with the indicated doses of FluLaval (FluL) 2016–2017 and boosted 3 weeks later. After another 3 weeks animals were infected i.n. with influenza A/California (A/Cal) at 10⁷ TCID₅₀ per 100 g animal and sacrificed one day later for analysis of viral load in the lung and nose. Results of viral titration by TCID₅₀ assay (VT) are shown. Control animals were infected i.n. with A/Cal and re-infected 6 weeks later (°2) or mock immunized and infected with A/Cal (°1). (b) One-time vaccination. Young and aged cotton rats were immunized with FluLaval once, infected i.n. with A/Cal 3 weeks later, and sacrificed 1 day after infection. Control animals were mock-immunized with PBS and infected i.n. with A/Cal once (°1) or twice with an interval of 3 weeks (°2) and sacrificed one day after challenge. Unimmunized and uninfected animals were included as additional controls (“-“). Results represent GMT±SE for 5–6 animals per group. *p < .05 when compared to primary infection of the same age animals, ^#p < .05 when compared to the same treatment, opposite age