| H1N1 had an R0 between 1.4 and 1.6 [1]. Let's assume it was 1.6. Let's assume that the current coronavirus has an R0 of just 2 (estimates vary, most higher than this). Perhaps it is less, but for the sake of argument lets say it's 2. 1.6^10 = ~110 2^10 = 1024 (so ~9x higher) That's with just 10 steps of transmission. So assuming the R0 of 2 is correct this will spread much faster. Now consider that people do not seem to show symptoms until at least 5 days after they've been exposed (by some estimates, even longer, like 9+ days). Assuming they are contagious at least part of that time, they are unknowingly spreading this. As others have mentioned add into it the fact that people who have been exposed to various flu viruses can have some immunity to new ones. Ignoring all that, just look what's actually happening on the ground in Italy and China. [1] https://www.ncbi.nlm.nih.gov/pubmed/19545404/ |