It is more realistic to assume that interventions to reduce R cannot be sustained indefinitely. If interventions are introduced, and subsequently removed before herd immunity has increased sufficiently to reduce R to approximately 1, this will postpone and diminish the peak incidence of the epidemic (though not necessarily the eventual attack rate), thus reducing the peak load on health services. Finally, we will argue that if the introduction of timelimited interventions (e.g. social distancing) is timed in such a way as to minimize the number of active infective cases as R approaches unity, then the minimum achievable attack rate can be obtained.