Figure 4.

Lung histopathology in the young and aged animals immunized with FluLaval 2016–2017 twice (a) or once (b). Animals were immunized or infected as described in the legend to Figure 3 and sacrificed 1 or 4 days after infection for analysis of pulmonary histopathology. (a) Pulmonary histopathology in influenza-infected animals after two-times immunization with FluLaval or 6 weeks after the initial infection with A/Cal. (b) Pulmonary histopathology in influenza-infected animals after one-time immunization with FluLaval or 3 weeks after the initial infection with A/Cal. Results represent GMT±SE for 5–6 animals per group. PB: peribronchiolitis, PV: perivasculitis, IP: interstitial pneumonitis, A: alveolitis. * p < .05: a decrease compared to primary infection of the same age animals; ^x p < .05: a decrease compared to primary infection of the same age animals; ^Δ p < .05: an increase compared to primary infection of the same age animals; ^@ p < .05: an increase compared to primary infection of the same age animals