Hemagglutination inhibition (HI) antibody titers before challenge and lung viral titers 3 days post-challenge with a homologous H5N1 reassortant virus in HAd-HA-NP-immunized naïve and HAd-primed mice.

Mice (10 animals/group) were inoculated i.m. or i.n. either with PBS (unprimed group) or with 107, 108, or 109 p.f.u. of WT HAd5 (HAd-primed). Subsequently, naïve and HAd-primed mice were immunized i.m. or i.n. twice at four week interval with HAd-HA-NP. HAd-primed mice inoculated with HAd-ΔE1E3 (vector control) served as negative controls. Serum samples were obtained from all animals four weeks after the last immunization and analyzed by HI assay using a H5N1 reassortant virus and horse red blood cells. The titers are shown as geometric mean values (GM). Four weeks after the last immunization, mice from each group were challenged with 100-fold of 50% mouse infectious dose (MID50) of a H5N1 reassortant virus having HA and NA genes of A/Vietnam/1203/04 influenza virus. Three days post challenge mice were euthanized, and the lungs were collected. The lung viral titers were determined to evaluate the protective efficacy of the vaccine. The detection limit of the lung viral titer was ≥1.5 Log10 EID50/ml. HAd, human adenovirus; WT, wild type; i.m., intramuscular; i.n., intranasal.