As the additional control measures announced recently take effect, we hope that R may be pulled down further - perhaps to 1.1 or lower. With R at such low levels, even limited accumulation of population immunity will start reducing the average susceptibility of the population, slowing transmission. When R is 1.1, only 9% of the remaining susceptible (i.e. not previously infected) population need to be infected for R to fall to 1, solely as a result of the natural dynamics of the epidemic. At this point, in some sense, population immunity has caused the epidemic to plateau. However, this is very different from a classic “herd-immunity” scenario, where an epidemic has run through a population with limited impact of control measures: