In addition, in Figures S3 and S4 , red ellipses have been added to show where similar HA and NA sequences from other, non-Hong Kong locations have clustered with Hong Kong sequences on the same branch. The dates of such sequences may be the same (within the limit of the one month temporal resolution used in this study), relatively similar, or very different. These highlighted clusters serve to demonstrate the mobility and ubiquity of this influenza A(H3N2) virus, worldwide, during this 10-year period, i.e. genetically similar viruses can appear in different parts of the world at similar and also different times. These examples are not meant to be exhaustive and other such examples may be found in these trees.