One parameter can be determined immediately from the multiple-cycle viral yield results. The viral titer decay rate, characterizing the decline of the virus concentration after the peak (Figure 3 ), corresponds to the slowest of the rate of loss of virus-producing cells and the rate of viral infectivity loss [37] . Since prior in vitro experiments have shown that infectious cell death is nearly complete shortly after the viral titer peak [38, 39] , we set the rate of viral infectivity loss, c, equal to the viral titer decay rate. Because this decay rate was determined to be 0:19h {1 for both A/Brisbane/59/2007 strains, we have fixed the rate of viral infectivity loss to this value for all simulations. This corresponds to a virion half life of approximately 3.6 h, which is consistent with prior measurements for influenza virus in the experimental literature (see, e.g., [35, 40] ). Having fixed the rate of viral infectivity loss, we are left with four undetermined parameters and two experimental measures.