The truth is we don't have enough data to currently know exactly what the transmissibility is. They did a study on the Princess Diamond cruise ship and found that on average, each person would infect 2.28 others. This is known as the "R-Nought." The seasonal flu has an r-nought value of about 1.3. So the average infected person with the normal flu will infect 1.3 others. Some studies have the Covid 19 r-nought value higher, at almost 3. The WHO estimates it between 1.3 and 2.5.
I don't think I've seen a single study showing its transmissibility is lower than the seasonal flu.
http://www.cidrap.umn.edu/news-persp...-23-death-rate
It's important to know that environmental factors play a role in this number. Are the dynamics on a cruise ship the same as the real world? Probably not. Then again, is the population of a cruise ship healthier and more resilient to catching a virus than the general population? Maybe, maybe not. We need time and data to study these things.
So, in a nutshell, that's the cause of the fear. At best, it transmits the same as the seasonal flu, but kills at a rate 20x higher. At worst, it transmits about double the seasonal flu, and still kills 20x as many infected.
As to why China isn't experiencing many millions infected...well they put in place some of the most severe measures to stop the spread of a disease than any country ever has before. They put an entire province under quarantine, complete with drones that would identify people who were moving around. They built multiple hospitals in 10 (TEN!) days.
https://www.sciencemag.org/news/2020...ther-countries
But if you think they did all that because of the western media, well, more power to you I guess.