The 10 years thing is probably a general time frame, not exactly 10 years on the dot. Also who says this games story had to be set exactly on that date? The storyline could drag on for 3-5 years for all we know. Or maybe it's a typo.
We don't know enough about the story to make any conclusions. For all I can tell, there is an outbreak in tall oaks, a chinese city, and a rural snowy village. It isn't necessarily a worldwide pandemic, just a worldwide scare, which wouldn't take much to produce.
Also, its been confirmed that Leona and Chris's stories are simultaneous. Not separate.
Remember... if it's slightly complicated, there is a wikia for it.