Fig. 1.

Time series of IPDs, ILIs, and climate in mainland France, 2000/wk 27 to 2010/wk 26. (A) Weekly number of IPDs in different age groups. For visual clarity, the y axis values differ between panels. (B) Weekly incidence (per 100 population) of ILIs in different age groups. (C) Weekly values of climate. The meteorological variables considered were the average temperature, vapor pressure (a measure of absolute humidity), relative humidity, and duration of insolation. We here represent the values of the first two components derived from a principal component analysis (PCA); these two components captured about 97% of the variability and were used instead of the individual variables in all of the analyses (see SI Appendix, Supplementary Methods for further details on the PCA).