Table 4. Predictors of seasonal A(H3N2) epidemic size, peak incidence, transmissibility, epidemic intensity, and subtype dominance.

Variables retained in the best fit model for each epidemic outcome were determined by BIC.

Outcome	Best Minimal Model1	R2	Adj. R2	RMSE
Epidemic Size	H3 epitope distance ($t$ – 2) + H1 epidemic size + H3 epidemic size ($t$ – 1)	0.74	0.69	9.88
Peak Incidence	H3 epitope distance ($t$ – 2) + H1 epidemic size + Dominant IAV Subtype ($t$ – 1)	0.69	0.63	2.09
Effective Rt	HI log2 titer distance ($t$ – 2) + H1 epidemic size + N2 distance to vaccine strain	0.69	0.63	0.11
Epidemic Intensity	HI log2 titer distance ($t$ – 2) + N2 distance to vaccine strain + vaccination coverage ($t$ – 1)	0.79	0.75	0.07
Subtype Dominance	H3 epitope distance ($t$ – 2) + N2 epitope distance ($t$ – 1) + Dominant IAV Subtype ($t$ – 1)	0.56	0.48	0.2

¹Candidate models were limited to three independent variables and considered all combinations of the top 10 ranked predictors from conditional inference random forest models (Figure 8).