The timing of one-shot interventions for epidemic control

Abstract

The apparent early success in China's large-scale intervention to control the COVID-19 epidemic has led to interest in whether other countries can replicate it as well as concerns about a resurgence of the epidemic if or when China relaxes the interventions. In this paper we look at the impact of a single short-term intervention on an epidemic. We see that if an intervention cannot be sustained long-term, it has the greatest impact if it is imposed once infection levels have become large enough that there is an appreciable number of infections present. For minimising the total number infected it should start close to the peak so that there is no rebound once the intervention is stopped, while to minimise the peak prevalence, it should start earlier, allowing two peaks of comparable size rather than one very large peak. In populations with distinct subgroups, synchronized interventions are less effective than targeting the interventions in each sub-population separately.We do not attempt to clearly determine what makes an intervention sustainable or not. We believe that is a policy question. If an intervention is sustainable, it should be kept in place. Our intent is to offer insight into how best to time an intervention whose impact on society is too great to maintain.

Indications for healthcare surge capacity in European countries facing an exponential increase in coronavirus disease (COVID-19) cases, March 2020

“…Remuzzi and Remuzzi reported on 12 March 2020 that in Italy, bed occupation in intensive care units (ICU) would exceed capacity [2]. From around the same time, other countries increasingly implemented large-scale interventions such as household isolation and school closures [3,4]. Important urgent questions as the epidemic unfolds are: (i) how close are other countries from reaching a pressure on the health system comparable to countries ahead of them and how should this impact their suppression and/or mitigation strategies, (ii) which countries are closest to such a situation and how should this impact international mobilisation of urgent logistical support, and (iii) what pressure will countries experience at the peak and how will that pressure affect treatment of cases.…”

Optimal, near-optimal, and robust epidemic control

“…Avoiding collapse of the healthcare system is the most valuable goal. What is more, among non-eradicative interventions, those that reduce the highest epidemic peak (almost) necessarily reduce the total case count (or "final size") of the epidemic, though they may not do so as efficiently as interventions specifically targeted at final size reduction [2].…”

“…There have been relatively few modeling studies on time-limited strategies for peak reduction. One known result establishes that time-limited peak reduction interventions should start earlier than final size reduction interventions, all else equal [2]. But the optimal strategy to reduce the peak not known, nor is the robustness of such a strategy to implementation error.…”

“…Locking down transmission too early and too aggressively slows the depletion of susceptibles. If controls are then relaxed too soon, there will be a large second epidemic peak [2]. This gives us some intuition for the importance of timing, and for the properties of the optimal intervention: it must trade off depletion of susceptible pool against reduction in the rate at which people become infectious.…”

Indications for healthcare surge capacity in European countries facing an exponential increase in COVID19 cases

“…Remuzzi & Remuzzi reported on March 12 th that in Italy ICU bed occupation would exceed capacity [1]. From around the same time, other countries increasingly implemented large scale interventions such as household isolation and school closure [2,3]. Important urgent questions as the epidemic unfolds are (a) how close other countries are from reaching an Italy-like pressure on the health system, (b) which countries are closest to such a situation, and (c) what pressure will countries experience at the peak and how will that pressure affect treatment of cases .…”