system
Given the following post, respond as if you're commenting on Reddit:
human
What does the R_0 value really mean?

Hey guys,

I'm currently reading up on viral outbreaks and I'm asking myself how I need to interpret the R\_0 values for different viruses that you can find online.

It is the number of people that get infected by one person when no one is immunized and no measures are being taken to contain the virus. So far, so good.

But at which timeframe do I need to look at?

Let's say that the R\_0 value for measles is 15. Does this mean that one person infects 15 people in one day and on the second day 225 people have been infected?

Or do I need to take the incubation period into account when looking at the various R\_0 values? Assuming that it takes four days for a person that has just been infected with measles to become infectious. Would that mean that it would take 8 days for 225 people to become infected?

Thanks!
gpt
R\_0 refers to the total number of other people a patient will infect *before either recovering or dying*. There's a separate number, typically referred to as "generation time", which tracks how long it takes from exposure to (on average) infecting someone else. You need both numbers to model a pandemic.