There was a high level of variability between the excess of mortality experienced in the 14 countries we studied, with a minimal value of 33% in Finland and a maximal value of 172% in Italy. Ninety years later, the reasons for this variability are difficult to investigate. We pointed out that there was a clear north–south gradient, but did not find a rationale for this gradient. All factors that can be related to the mortality burden such as the existence of co‐infectious diseases, especially bacterial pneumonia and tuberculosis, or socio‐economic status were unlikely to have a north–south gradient. Possible geographic determinants of the influenza mortality are cold temperature and vitamin D deficiency relative to low sunlight exposure, but they would have implied a higher mortality in northern countries, not the opposite as we observed.