Originally Posted by
73qanda
Mick, That’s an interesting observation to a layman like myself. Why is it that such a high RO doesn’t result in pandemic? Is it to do with established immunity?
For measles, yes, immunity via the MMR vaccine is a, if not the, key factor.
It's also important to understand what R0 actually represents. It
is a measure of potential transmissibility. Importantly, it does not tell you anything about how fast a disease will spread.
And you need to remember that R0 is an average. So if a virus has an R0 of 2 this could mean that every single infected person passes the virus on to two other people. Or, it could also mean that one infected person is what is known in epidemiology as a “super-spreader” and that one person infects 100 people, while 49 other infected people infect no one. You get an R0 of 2 in both scenarios. However, the consistent 1:2 infection scenario and the super-spreader scenario have radically different implications for what will happen during an outbreak. Other coronaviral diseases, such as SARS and MERS, involved super-spreader events. We don't have enough data to say the same for 2019-nCoV.