I believe that the American panic reaction was in response to the Chinese panic. The Chinese government approached it as if they had loosed something they thought they knew was a major Plague type killer. A naturally occurring virus would have been just allowed to pass through society like any other flu. It is apparently much less lethal than the Chinese government expected. Chinese actions re: the virology lab suggest strongly they believe it to have come from there.
But it achieves their goal of culling the weak and elderly, while most "workers" recover.