Understanding the factors that influence the circulation of seasonal influenza viruses is a major public health challenge. By analysing 9,604 viral haemagglutinin (HA) sequences from the 2 influenza A subtypes H1N1 and H3N2, and the 2 influenza B viruses Yamagata and Victoria (all of which cause annual epidemics), Bedford et al. now show that the global circulation patterns of these viruses differ considerably. H1N1 and the two influenza B viruses persist locally between epidemics, whereas H3N2 viruses tend to be more widespread globally but die out between epidemics. Interestingly, H1N1 and the influenza B viruses showed slower rates of HA evolution compared with H3N2 viruses. Modelling suggests that because H1N1 and influenza B viruses evolve more slowly and mainly infect children, whereas H3N2 viruses evolve rapidly and infect individuals of all ages, the less frequent travel of children may be a factor that limits the global spread of H1N1 and influenza B viruses.