China releasing a bioweapon intentionally on its own citizens doesn't make sense. Its either an accident or some foreign power: The problem is, viruses don't respect borders and spread to foreign power lands. Accidental release of research virus also doesn't make sense, such things are not built to be super-AIDS, they're altered for the exact purpose of research, like adding/removing some genes.
It must be some group that want to cripple rest of humanity and has the means to counteract the effect of the virus(probably vaccines?). A government agency can't operate on this level of autonomy. It can only be a secret society...