Internal branches with high average antigenic weights (≥1.0 antigenic units) and according antigenic types in comparison to antigenic clusters identified by antigenic cartography (branches leading to three or less isolates are excluded).

Branch amino acid changes indicate the corresponding branches, where changes in bold were also found by Smith et al. (2004), and weights give the respective up, down and average branch weights. Multiple branches that can be mapped to a single antigenic type are separated by dashed lines. Additional amino acid changes indicate branches that carry further mutations found to be cluster transition substitutions by Smith et al. (2004). For some branches, the down-weight was not defined, as no antiserum was in the respective subtree. Branches that can be mapped to multiple type transitions are shown at the first mapping only. Smith et al. (2004) present average distances between consecutive antigenic clusters, whereas average antigenic branch weights give a minimum distance between consecutive antigenic types. Note that on branches with multiple changes not all changes have to contribute to the antigenic weight, though their individual impacts could not be resolved with the dataset (unsampled viral isolates).