Figure 3 presents the fitness between the reported attack rates and predicted infection risks in different scenarios, while Table 1 lists the scenarios with the best fitness (the minimum RSS) for the seven types of serving pathways. According to the dose-response relationship model , the infection risk increased with the viral load, L0, and the dose-response parameter of the mucous membranes, ηm. Excessively small or large values of these two parameters yielded correspondingly too low or high infection risks that deviated considerably from the attack rates. Therefore, the best fitness was reached with moderate values of ηmL0, as shown in Figure 3 and Table 1.