It wasn't. Countries like Italy and Germany believed China, and that alone would probably have been enough to doom efforts in the countries that didn't. Also, a

It wasn't. Countries like Italy and Germany believed China, and that alone would probably have been enough to doom efforts in the countries that didn't. Also, as the other reply says, patient zero was likely already in the US, so any effort at successfully containing this would have required rounding up and quarantining people from Hubei already in the USA and their close contacts back when the press were still downplaying it. (That's effectively what China did, though it was... a little ugly, shall we say.)