What makes you think China doesn't want some of it's side taken out? What is the China policy on having children again?
Absolutely, China doesn't worry about losing half their population. What China does worry about is loss of investment and business. Still building military machine, check back in five years.
I would suppose that if you wanted to eliminate an enemy, you would design a biological weapon with greater than 4% lethality. Also, you would want the disease to have a short incubation/duration period; so not to flood your hospitals with the sick. The average hospital stay for this is on the order of 10 days; and then there is a substancial liklihood of permanent lung tissue damage. It's serious, but not a weapon. It's far morelikely to turn on your own troops, than the population you wish to attack. Aas your troops tend to bunk together, eat together and live together.