06 July 2021
Since the start of the pandemic, countries have heavily invested in the development of control strategies that aim to contain the spread of SARS-CoV-2 while limiting as much as possible their impact on economic and social activities. Like many other European countries, France implemented a lockdown of its population on 17 March 2020, which led to a 77% drop in SARS-CoV-2 transmission rate and a reduction in daily ICU admissions from 700 in late March to 44 on 11 May. The lockdown was then replaced by less restrictive physical distancing measures, the general use of face masks and the implementation of an approach based on the detection, testing and isolation of cases and their contacts. To cope with a rebound of the epidemic, a new lockdown was implemented in November 2020.
Thorough monitoring of the epidemic is essential to quickly detect possible epidemic rebounds and, if needed, implement corrective measures. When a local surge in cases has been identified, authorities in Germany, Portugal, the United Kingdom or Australia have not hesitated to quickly impose local lockdowns. However, given the major economic and societal costs associated with general lockdowns, the decision may be more difficult in scenarios where the number of cases grows slowly in a wide area. In such circumstances, authorities might prefer strengthening control measures without going as far as a general lockdown, for example with extended curfews, hoping this will be sufficient to contain spread at a lower cost for society. However, should these alternative control measures be unsuccessful, a new lockdown could be a last resort.
A new RECOVER study developed a modelling framework to help policymakers assess the use of lockdown as a last resort option, by determining when a lockdown should be adopted to avoid passing a predetermined ICU capacity target and by evaluating situations where a slowly growing epidemic might remain manageable for the healthcare system without the need for a lockdown. This was done for a broad range of rebound scenarios that are characterised by their doubling time (i.e. the time it takes for the daily number of cases to double) and exploring the many uncertainties that remain. The study illustrated this framework in the context of metropolitan France.
The daily incidence of ICU admissions and the number of occupied ICU beds are the most robust indicators to decide when a lockdown should be triggered. When the doubling time of hospitalisations estimated before lockdown is between 8 and 20 days, lockdown should be enforced when ICU admissions reach 3.0– 3.7 and 7.8–9.5 per million for peak targets of 62 and 154 ICU beds per million (4,000 and 10,000 beds for metropolitan France), respectively. When implemented earlier, the lockdown duration required to get back below a desired level is also shorter. These simple indicators and triggers help to decide if and when a last-resort lockdown should be implemented to avoid saturation of ICU. These metrics can support the planning and real-time management of successive COVID-19 pandemic waves.