Two recent papers [37, 38] have suggested that the existing evidence tends to support a migration rather than a latency mechanism to explain the annual seasonality of influenza A. However, they did not have access to large numbers of influenza sequences from Southeast Asia. Thus, in view of the new data presented in this study, it is hoped that such hypotheses may be revised, to include a contribution from the latency mechanism. In some populations (perhaps those more localized in Southeast Asia), this latency mechanism may contribute more significantly to the underlying basis for the seasonality of influenza A -a possibility not entirely ruled out by one of these studies [38] . More data is required to explore this hypothesis in those populations. Admittedly, the fact that in this 10-year (1997-2006 ) data set of almost 300 influenza A(H3N2) HA and NA sequences from Hong Kong, we have only found one particular example supporting the latency mechanism, does suggest that this is a relative rarity, and that the migration mechanism is probably responsible for the majority of influenza seasonality patterns seen worldwide.