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Figure 3. Expected relationship between outbreak size (as fraction
of the population affected) and 2 key epidemiologic parameters: I0
is the number of primary cases of infection introduced into the human
population from an external source such as a zoonotic reservoir (increasing
in the direction indicated); R0 is the basic reproduction
number, a measure of the transmissibility of the infection with the human
population (see text). The curves are obtained
from a modified version of the Kermack-McKendrick equation and show that
expected outbreak size is particularly sensitive to small changes in I0
or R0 when R0 is close to 1. Examples
of zoonotic pathogens with R0>1, R0<1
and R0 close to 1 are shown. RIVF, Rift Valley fever
virus. (Reprinted with permission from [23]).
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