The lockdowns cometh

This paper appears to be the primary rationale behind the nationwide lockdowns that are being gradually imposed by governments around the world:

The optimal timing of interventions differs between suppression and mitigation strategies, as well as depending on the definition of optimal. However, for mitigation, the majority of the effect of such a strategy can be achieved by targeting interventions in a three-month window around the peak of the epidemic.  For suppression, early action is important, and interventions need to be in place well before healthcare capacity is overwhelmed. Given the most systematic surveillance occurs in the hospital context, the typical delay from infection to hospitalisation means there is a 2- to 3-week lag between interventions being introduced and the impact being seen in hospitalised case numbers, depending on whether all hospital admissions are tested or only those entering critical care units. In the GB context, this means acting before COVID-19 admissions to ICUs exceed 200 per week.

Perhaps our most significant conclusion is that mitigation is unlikely to be feasible without emergency surge capacity limits of the UK and US healthcare systems being exceeded many times over. In the most effective mitigation strategy examined, which leads to a single, relatively short epidemic (case isolation, household quarantine and social distancing of the elderly), the surge limits for both general ward and ICU beds would be exceeded by at least 8-fold under the more optimistic scenario for critical care requirements that we examined. In addition, even if all patients were able to be treated, we predict there would still be in the order of 250,000 deaths in GB, and 1.1-1.2 million in the US.

In the UK, this conclusion has only been reached in the last few days, with the refinement of estimates of likely ICU demand due to COVID-19 based on experience in Italy and the UK (previous planning estimates assumed half the demand now estimated) and with the NHS providing increasing certainty around the limits of hospital surge capacity.

We therefore conclude that epidemic suppression is the only viable strategy at the current time. The social and economic effects of the measures which are needed to achieve this policy goal will be profound. Many countries have adopted such measures already, but even those countries at an earlier stage of their epidemic (such as the UK) will need to do so imminently.

Basically, the less strict the measures, the more likely it is that the number of people requiring treatment will overwhelm the available medical serves at the peak. Hence the term “flattening the curve” which refers to the peak of the bell curve. Different nations are at very different risk in this regard; Germany has 25,000 ICU beds with full respiratory support, or one for every 3,312 people, vs 4,000 for the UK, or one for every 16,610 people.

The USA has 32,000 ICU beds, which puts it right in between at one ICU bed for every 10,000 people. This means that if the mitigation calculations are correct, the medical resources would be overwhelmed by a factor of 8x, thereby leading to fatalities in excess of 2 million. The suppression measures are expected to reduce that by three orders of magnitude, which is why it is safe to expect that they will be imposed, sooner rather than later, in the US, the UK, and other countries that have not yet officially adopted them.

UPDATE: As expected, the UK announced a three-week nationwide lockdown.