Initial H7-Hemagglutinin Tree
Eurasian H7-HA (segment 4) from avian complete genome sequences, and the new H7N9 NA sequences were analysed in BEAST, using the SRD06, relaxed log normal clock and GMRF skyride. The estimated time to most recent common ancestor of the H7 hemagglutinin of the new human cases is 2011.77 (HPD:2010.3 - 2012.66).
The most recent common ancestor of the new H7 and N9 sequences seem similar, and are approximately between 2011.5 - 2012 (although these initial trees are very preliminary). It could be that this strain has been circulating, presumably in poultry for about 1 year before the first human cases have been detected.