China the center point of largest pandemic threat in the last 100 years
Aren't they always?
Not always, and opinions & theories vary about some places of origin.
1918 Spanish Flu pandemic - some say Etaples, France was center of the global pandemic, while it originated in Kansas. The first confirmed outbreak did occur in Kansas at a military base. Others say the origin of the pandemic was Austria; others say China.
1968 H3N2 pandemic - Hong Kong was place of origin
2009 H1N1 pandemic - originated in Mexico
All of those subtypes are swine with avian & human genes. The 1918 Flu was an H1N1 swine subtype, but it had avian origins. Some theorize it had equine origins. All of the human flu pandemics in recorded history have been primarily swine subtypes.
The H7N9 subtype in China, right now, is avian. It would probably have to reassort with a swine subtype to become more human-to-human transmissible, at least, according to historical pandemics.