Fig. 1: The effects of influenza epidemic dynamics in preceding seasons on subsequent epidemic composition and size.

a The distribution of lull period durations, in number of seasons, by (sub)type, across all countries and seasons. A lull duration of zero corresponds to the same (sub)type’s substantial circulation in the previous season and the current season. b The distribution of relative epidemic sizes by virus (sub)type, across all countries and seasons. c The relationship between the number of seasons since previous substantial circulation of a (sub)type and the probability of the (sub)type’s substantial circulation. Error bars correspond to 95% confidence interval from an exact two-tailed binomial test for proportions. Points correspond to point estimates of the probability. The probabilities were computed from all countries and seasons (n = 642, 460 and 624 country-season pairs for A/H3N2, A/H1N1pdm09, B, respectively). d Relationship between the relative size of a (sub)type-specific epidemic and the number of seasons since previous substantial circulation of that (sub)type. Each point corresponds to a specific country, in a specific season (n = 188, 198 and 186 country-season pairs for A/H3N2, A/H1N1pdm09 and B, respectively). Points are coloured by the season. Boxplots show the median and first and third quantiles. Whiskers correspond to the minimum of the maximum value and the third quartile + 1.5 × the interquartile range for the upper whisker, and the maximum of the minimum value and the first quartile − 1.5 × the interquartile range for the lower whisker. e Relationship between the relative size of a (sub)type’s epidemic and (1) the size of that (sub)type’s epidemic in the previous season (left); and (2) the sum of the two previous seasons’ sizes of that (sub)type (right). For each of the two subpanels, each point corresponds to a specific country, in a specific season (n = 180 country-season pairs for each (sub)type for previous season size, n = 160 for each (sub)type for previous two seasons size sum). Points are coloured by the season.