Table 2.

H3N2 risk level forecasts for the US based on the cluster model. Seasonal risk level for H3N2 influenza virus is defined as high or low for each season from the out-of-fit period (2011–2017) compared to a reference level defined as the 50% quantile of the seasonal total H3N2 incidence cases in the corresponding training dataset. We defined an observed season as H3N2 high risk, when the observed total H3N2 incidence surpasses the reference level; and a H3N2 low risk season otherwise. For the forecasts, the percentage of 1000 simulations that exhibit a H3N2 high risk was obtained. When this percentage exceeded 40% (chosen based on Fig. S5), we forecasted a H3N2 high risk season. Otherwise, a H3N2 low risk season was predicted.

Seasons	Observed	% High(1000 simulations)	Forecasts (>40%: high)
2011/2012	Low	8.2	Low
2012/2013	High	99.6	High
2013/2014	Low	3.6	Low
2014/2015	High	99.9	High
2015/2016	Low	7.0	Low
2016/2017	High*	100.0	High

^*Based on the updated data from the weekly US influenza surveillance report until week 14 ending on April 8, 2017