The contrasting phylodynamics of human influenza B viruses.

A complex interplay of viral, host and ecological factors shape the spatio-temporal incidence and evolution of human infuenza viruses. Although considerable attention has been paid to infuenza A viruses, a lack of equivalent data means that an integrated evolutionary and epidemiological framework has until now not been available for infuenza B viruses, despite their significant disease burden. Through the analysis of over 900 full genomes from an epidemiological collection of more than 26,000 strains from Australia and New Zealand, we reveal fundamental differences in the phylodynamics of the two co-circulating lineages of infuenza B virus (Victoria and Yamagata), showing that their individual dynamics are determined by a complex relationship between virus transmission, age of infection and receptor binding preference. In sum, this work identifies new factors that are important determinants of infuenza B evolution and epidemiology.