In order to assess antibody titres immediately before challenge, mice were vaccinated with different doses of each vaccine and serum was obtained 25-days post-immunization. HI reciprocal titres of 9866326, 10936293, and 1280 for the PAV3-HA vaccine or 10666330, 10666330, and 11736261 with AdHu5-HA were detected for 10 8 , 10 9 or 10 10 vp/mouse doses respectively (Figure 2c ). Both vaccines had similar HI antibody titres at all doses, with no significant differences detected between the PAV3-HA and AdHu5-HA (p = 0.57). Based on clinical data, a reference HI antibody titre of 40 is recommended for influenza vaccine candidates as the minimum level to confer fifty percent protection in humans [24, 25] . Both vaccines met this requirement at all doses prior to challenge. Serum samples had an average NAB titre of 65620, 75614, or 106646 reciprocal dilution at 10 8 , 10 9 or 10 10 PAV3-HA vp/mouse respectively ( Figure 2d ). The AdHu5-HA vaccine generated NAB titres of 65620, 55620 or 133646 at 10 8 , 10 9 or 10 10 vp/mouse, respectively.