Figure 2.

Protection against lethal challenge with historical influenza A viruses. BALB/c mice were divided into two experimental groups: H1-HA and H3-HA groups. All groups were intramuscularly (IM) prime/boost immunized with different vaccines at 0- and 21-days post-vaccination (DPV), as previously mentioned. At 35 DPV, mice were intranasally challenged with 20 µL of 10 MLD₅₀ of mouse-adapted influenza A viruses including A/Puerto Rico/8/1934 (H1N1), A/Fort Monmouth/1/1947 (H1N1), A/Texas/1/1977 (H3N1), and A/Aichi/2/1968 (H3N2). Mice were monitored daily for weight loss for 14 days and euthanized when they lost 25% of their starting weight.