As a stone thrown in a still pond : predicting human influenza epidemiological dynamics after 2009 A/pH1N1 pandemic explosion

Seasonal influenza exhibits well-recognized epidemiological patterns. Tropical regions have been demonstrated to serve as the epicentre from where seasonal influenza virus drift variants of the A/H3N2 subtype are fuelled into temperate climate regions. In a global prospective cohort study (IRIS), carried out between 2009 and 2013, we collected over 2,000 A/H3N2 and A/H1N1 viruses from patients with uncomplicated influenza. We estimated the effective reproductive number (R0) from phylogenetic tree applying phylodynamics models. In addition, we reconstructed the order of migrations events between geographical partitions using a discrete-trait phylogeographic model which – for the first time – allowed to gain spatio-temporal resolution on the migration dynamics at a global level after the pandemic explosion of A/pH1N1 in 2009. We have formulated a hypothesis about the amplitude and frequency of R0 oscillations which resemble those observed by throwing a solid in the water (”stone-in-the-pond” theory). Moreover, differences in the circulation patters between A/pH1N1, A/H3N2, and B strains appeared to be correlated with R0 fluctuations. While contributing to our understanding of global seasonal influenza epidemiological effects, these observations may also be crucial for predicting the appearance of the next pandemic influenza strai