The two epidemiologists had gathered the data from the Mexican outbreak. They estimated the attack rate—the percentage of the population likely to be infected—at somewhere between 20 and 30 percent, and the so-called case fatality rate at between 0.1 and 1.8 percent. That was the difference between a slightly worse than usual flu season and more than one million dead Americans, some large number of them children. With that little information, decisions had to be made.
