Figure 6. Comparison of simulated age class–specific illness attack rates with past pandemics. Simulated illness attack rates (half the infectious attack rate) for the unmitigated base case are close to those found in studies of historic pandemics in 1957 (19), 1968 (20), and 1918 (21). Notable differences are the 1968 Hong Kong flu, which had less effect on youth and 1957–58 Asian flu, which had greater effect; however, historic data are inherently uncertain. Closer correspondence to either of these 2 cases could be achieved through changes in IA or SA or modification of the underlying social contact network (see Results) because the network was likely different from that of a small town of today.