where T(r,t) and I(r,t) are the densities of target and infectious cells, respectively, and V (r,t) is the virus concentration. s (20-fold smaller than the Stokes-Einstein value for a 100 nm particle in 37 0 C water); the rate of viral infectivity loss was fixed at c~0:19h {1 based on the observed viral titer decay rate for both A/Brisbane/59/2007 strains in the multiple-cycle viral yield assays (see Results); and the infectious lifespan was held fixed at 12 h (Table 1) . Simulations were initialized with a ''top-hat'' central region of infectious cell density with radius d cell =2, and with all other cells in the target state. All fields rapidly take the form of traveling waves T(z), I(z) and V (z), where z~r{vt, with the same velocity, v.