Figure 2
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The epidemic size ζ
as a functionof the basic reproduction ratio 
in the simplest SEIR model corresponding to (2.6)–(2.9) exhibits a clear phase transition at
(thick curve). The other curves represent r(t) taken for t =30, 60, 90, for which equilibrium is not yet achieved. In practice, varying 
is achieved by acting on the q
factor in (2.25)–(2.28).
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