We tested our algorithm for its specificity (i.e., not detecting a pandemic when no pandemic is occurring). To do this, we first calculate WCR and N HB for each week from a given seasonal HB-level ILI time series. We obtain the probability values of weekly pairs of (WCR, N HB ) from the joint probability distribution (the plots of the weekly probability values are given in Figure 3 ). In the second step, for a chosen threshold probability value δ, we count the number of weeks in which the probability of (WCR, N HB ) falls below the threshold. The total counts represent the number of false alarms (Fa s (δ)) in season s. The theoretical maximum number of false alarms ( FA s max ) in any given season is the total weeks minus 1 because WCR cannot be calculated for the first week. Finally, this leads us to calculate the specificity of the detection algorithm for a given threshold probability as follows: