Hypothesis on a possible role of El Niño in the occurrence of influenza pandemics

The El Nino phenomenon is the Earth’s strongest climatic fluctuation on an interannual timescale and has a quasi-global impact, although originating in the tropical Pacific Ocean. A very strong El Nino is recognized to cause extreme dryness and wetness in different parts of the world. We show that all the eight well-documented influenza pandemics, starting from the first certain one documented in ad 1580, originated in China and in Russia, a few years after the occurrence of a very strong or after a prolonged strong/moderate El Nino event. At present, the next El Nino will probably occur at the beginning of 2013 (Mazzarella et al. Theor Appl Climatol 100:23–27, 2010), and this forecast may suggest to be well prepared to take appropriate precautionary epidemiological measures.