Figure 2a shows that all mice that were infected on day 0 with this nonlethal dose of PR8 survived. Another set of control mice that were mock infected on day 0 and then infected with Sp3 on day 7 exhibited ∼40% lethality, as expected. When mice were PR8 infected on day 0, vehicle treated on days 2 to 6, and then infected with Sp3 on day 7, there was a highly significant increase in lethality (∼90%), confirming that this is a robust model of influenza-enhanced susceptibility to 2° bacterial infection. Here, SP3 is linked to bacterial infectious disease.