Influenza Challenges
Four weeks after immunization, the mice were challenged intranasally with mouse-adapted influenza A/Puerto Rico/8/34 (PR8; H1N1). Groups of 10 mice were challenged intranasally (i.n.) on day 28. The mice were anesthetized intraperitoneally with ketamine/xylazine (2 mg ketamine and 0.15 mg xylazine) before i.n. infection with 10 µL of sterile saline containing PR8 (20 HAU/mouse). The protective efficacy of the immunization was measured by survival up to 14 days and mice that lost ≥ 25% of their initial body weight was euthanized according to institutional guidelines.