Temporal, geographic and genetic distribution of human cases of influenza H7N9. A) Evolution in the number of reported influenza H7N9 infections in humans caused by viruses from the Eastern cluster (similar to A/Shanghai/1/2013(H7N9) and the Southern cluster (similar to A/Guangdong/1/2013(H7N9)). B) and C) Geographic distribution of human cases during the first and second waves of the disease, respectively. The number of cases and their locations were obtained from the WHO case reports on influenza H7N9 (http://www.wpro.who.int/outbreaks_emergencies/H7N9.archive/en/). The genetic classification of the H7N9 clusters is based on the phylogenetic analysis of the viral isolates. Shaded areas represent the territories in which the presence of the virus has been detected by surveillance studies.