Question

in epidemic models what is R0? why is it important

Answer 1

The basic reproduction number, R0, is defined as the expected number of secondary cases
produced by a single (typical) infection in a completely susceptible population. It is important
to note that R0 is a dimensionless number.
.
Some authors incorrectly call R0 the “basic reproductive rate.”
We can use the fact that R0 is a dimensionless number to help us in calculating :--

Value of Ro characterises the ability of an infectious organism to invade into a virgin population ofsusceptible individuals. The quantity shows threshold behaviour.

More precisely, if Ro < 1 the infection cannot establish itself, and the outbreak of disease will only involve a very small number of individuals.

If Ro > 1 the infection can, at least initially, invade the population and cause an epidemic in the sense that there is a positive probability of a large outbreak.
Second, and more importantly, Ro is a measure to gauge the amount of uniform effort
needed for a given control measure to eradicate an infection that has already become
established in the population (i.e., that is endemic), and it measures the amount of
effort needed to prevent an epidemic.