When establishing animal models of viral respiratory infection, the optimal dose and route of delivery are critical to ensure reproducible outcomes. The mouse model for influenza infection is widely used due to the small animal size and simplicity of viral inoculation. During establishment of a mouse model of influenza A infection we observed a marked shift in morbidity when identical influenza A inoculum doses were delivered in less than 35 μL. We show for the first time that mice challenged with a 25 μL inoculum volume readily recovered following infection with an infectious dose of influenza A virus that was fatal when inoculated in 35 or 50 μL volumes.