There is a very good chance that we will not see just one wave of the pandemic in different geographical areas, but multiple.
Early, I talked about the reproduction rate of a disease, or R0. For the incident rate (number of new cases in the population) to fall, the R0 has to be less than 1, or to put it in English, each person with the disease has to spread it to less than one other person.
The R0 allows us estimate what level of either infection and recovery or vaccination is needed to provide sufficient herd immunity to stop disease transmission in a population. Fine et al. provided a model that is useful.
My takeaway with just an eyeball assessment of the graph is that we will need to have around 40-65% of the population immune through either illness and recovery or vaccination when that becomes available. My models have been based on only 20% of the population being infected. That is a terrifying thought based on how high the morbidity and mortality could be by increasing that attack rate by 2-3.5x what I had previously calculated for mortality or for the hospital surge model I’ve built.
Be prepared for the long haul with COVID-19. This is going to take months to well over a year.
Stay home. Stay safe.