Even when the R0 reaches 1.0 those who are infected will still infect one more person (on average). Infections continue to happen after the R0 is below 1.0.
Thanks, that does make intuitive sense. I wonder for a virus like SARS-CoV-2 that has a high R_0 and thus requires maybe 80% of the population to be immune for full herd immunity, if that means that the overshoot would be pretty mild?
It would mean the overshoot would likely go close to 100%, but it is complex to model as not everyone is equally likely to be infected - basically the population is not uniform. Epidemiologist do model this, but it requires relatively complex models.