The end of the social confinement in Spain and the COVID-19 re-emergence risk

Leonardo Lopez; Xavier Rodo

COVID-19 pandemic has entered a new stage in which the United States appears to be at the epicenter and Europe seems to have passed the peak of SARS-CoV-2 outbreak 1 . In this situation and whereas Italy decided not to yet lift lockdown measures, Spain after a large outbreak of still tens of thousand active cases, already plans for immediate deconfinement actions. Data on the last similar scale pandemic more than one century ago remains limited, despite aftermath reports exist 2 . The fact that the 1918 Spanish flu pandemic had a second deadly epidemic wave, presumably caused by strain mutations 3 , has also stimulated a vivid debate on whether actions to take now should or not incorporate this uncertain future. Under this scenario, optimal interventions on the COVID-19 pandemic aiming at a relaxation of strict social distancing enforcement are hard to fathom. More so, when the extent of pre-symptomatic and asymptomatic infections is not narrowly constrained (e.g. may be up to 86 percent 4 ). Europe's worst hit countries, Italy and Spain, are now seeing a flattening of their respective death tolls. On March 29, the Government of Spain published a decree that paralyzed all sectors considered non-essential in a draconian lockdown 5, 6 . The objective was to take advantage of Easter holidays to transfer the low level of mobility from Saturdays and Sundays to the rest of the days of the week, thereby reducing new infections and thus giving hospitals and ICUs a break when on the brink of collapse. Under an impending economic crisis, the Spanish executive government now believes it is time for the economy to recover a certain dynamism 7 . However, whether soon or later the return to normality should be attempted, the decision of when and how best decide to optimally move in that direction is at the center of worldwide debate 8 . This decision unfortunately presents a double problem in which two factors are related. First, there is a risk that the return to activity will end up causing a spike in infections that will aggravate the sanitary collapse at a time when the situation is still delicate. Second, there is no way to assess this risk, given the lack of existing information on the actual number of people infected or the real extent of immunity developed among the population. In both Spain and Italy active infections are still in the thousands, and a lift of lockdown makes the risk of a flare up in cases again a serious threat. According to the WHO, it is premature for Europe to think about a lack of confinement, given the number of active cases and waiting longer would be more prudent 9 . In the UK, for example, much of the industry is at a stop and these measures are expected to continue for at least two months 10 . On the other hand, confinement in the current circumstances seems to be working satisfactorily considering that the number of new infections and fatal cases is decreasing in these two countries. Re-allowing the mobility of a large number of the confined population might increase the risk that these figures will rise again. To this end, in this article, we present projections based on a modified SEIR model that allows simulating both the degree of population confinement and the different post-confinement scenarios. Our study intends to evaluate effects of different actionable scenarios for Spain and inform also other countries of the risk that each of these scenarios entails.