Viral evolution. A) Bayesian evolutionary chronogram for the time-labelled viral sequences sampled at the indicated dates. Note that the evolutionary tree evolves towards simplification and finishes simply as a backbone of a single branch. B) Viral effective population sizes as inferred after Bayesian skyline calculation; median value is shown in continuous line; dotted lines represent the 95% highest posterior density (HPD) interval around the median. Viral diversity decreases with time and plateaus after SCT. C) Pair-wise distances among sequences sampled at the corresponding dates, as inferred after maximum likelihood criterion using the GTR+Γ4 model.