Fig. 1: Weekly time series of environmental measurements and influenza activity in 46 states of the USA during 2010–2015.

Influenza activity is indicated by the variable “Flu” which is the product of two proportions: the proportion of influenza-like-illness cases among all clinical consultations in the community and the proportion of laboratory confirmed influenza-positive specimens among all specimens tested. Long stretches of 0 values for “Flu” in non-influenza season (June to September), shaded in gray columns, contain little information for causal inference and thus are omitted from data analysis.