Just nitpicking but attack rate and reproduction rate are not quite the same. The attack rate (which is not a rate but more a likelihood of getting sick if you're not
immune) refers to the fraction of people who get infected out of those who can
get infected. For example, measles (a very effective(*) and efficient(**) disease) has an attack rate of 90%+. This means if you're not immune and come into contact with a measles carrier, you'll most likely be infected.
(*) How much "force" the disease has or how easy it is to get infected once you get in contact. Ebola has a lot of force for example. (Hence the extreme bio measures taken. The flu does not have a lot of force.
(**) How much "reach" the disease has, that is how long it lingers in the environment or how far away it spreads or whether it's airborne. Ebola has almost no reach. As long as the patient stays 10-15ft away out of sneezing distance, you're good. Measles are very efficient (as long as you're breathing the same air---IIRC the longest confirmed distance for a measles infection was ~200ft
). The flu is semi-efficient (touch a door handle followed by your nose).
The reproduction rate is about how many get infected out of ALL the people (including those who are immune, isolated, and susceptible). The reproduction rate will vary as these numbers change (e.g. people get well and become immune, people get vaccinated or isolated, or they die). If the reproduction rate remains >1 the epidemic has positive feedback and the number of cases increase. If the reproduction rate is <1, the feedback is negative and disease dies out eventually.
Another way to think of it is that vaccination reduces the reproduction rate (which has to get under 1 for the vaccination program to be effective) but it does not reduce the attack rate because the attack rate is inherent to the disease.
R0 refers to how fast it's spreading initially, that is, how inherently good the disease is at its job in a "fresh" population of humans. It's a basic parameter in the SIR-model. See http://mathworld.wolfram.com/Kermack-Mc ... Model.html
So the Wuhan virus is literally ~3 times better than other big flus. This means it will be that much harder to contain. I did read elsewhere that it's not as lethal as SARS.
PS: I find this stuff fascinating in the way that a recovering astrophysicist dealing in similar dynamic modelling might. I enjoyed creating the cancer/enzyme simulations I did some years ago. I'd even consider working in theoretical epidemiology if I knew of a way in. Unfortunately, I don't think it's like coding where they'll just hire people off the street based on skill.