With something as contagious, and an incubation period as long as the coronavirus, I doubt any country in the world would have had any luck in stopping this it from becoming a pandemic,
with new estimates of the virus r0 being between 4.7-6.6, which is massive since the Spanish Flu and H1N1 only had r0 of approximately ~2 or less.
The novel coronavirus (2019-nCoV) is a recently emerged human pathogen that has spread widely since January 2020. Initially, the basic reproductive number, R , was estimated to be 2.2 to 2.7. Here we provide a new estimate of this quantity. We collected extensive individual case reports and...
www.medrxiv.org
How fast do you think people can diagnose a novel outbreak when the symptoms are so similar to the flu? Now compare the actions China took compared to the actions of the US during the H1N1 outbreak in 2009. China locked down everything when there were only 600 confirmed cases (later estimated to be around 2500 cases). Whereas the US didn't lock down anything, pretty much didn't take any action and the president only declares a National Health Emergency ~7 months after the first cases were identified, which by then the CDC reports: "The CDC estimates that 22 million Americans have gotten the virus".