The H7N9 subtype of the influenza A virus is a relatively recent infectious human pathogen. Normally a type of avian influenza, H7N9 has not caused the influenza disease until March 2013 in China. The WHO reports in February 2017 a total of 1222 human cases, with a mortality of about 40 percent. Early findings suggest the virus is transmitted mainly from domestic poultry and from person-to-person only in rare cases. H7N9 antibodies typically recognize hemagglutinin and neuraminidase antigens expressed on the viral envelope surface.