Abstract
Lockdown curbs the COVID-19 epidemics but at huge costs. Public debates question its impact compared with reliance on individual responsibility. We aim at understanding how rationally chosen self-protective behavior impacts the spread of the epidemics. We want to, first, assess the value of lockdown compared to a counterfactual that incorporates self-protection efforts under unknown disease prevalence; and second, assess how individual behavior modify the epidemic dynamics when mandatory policies are relaxed. We couple an SLIAR model, that includes asymptomatic transmission, with utility maximization: Individuals trade off economic and wellbeing costs from physical distancing with a lower infection risk. Effort depends on risk aversion, perceptions, and the value of contacts. In a Nash equilibrium, individual uncoordinated efforts yield average contact intensity, which drives epidemic transmission. Equilibrium effort differs markedly from constant, stochastic or proportional contacts reduction. It adjusts to reported cases in a way that creates a slightly decreasing plateau in epidemic prevalence. Calibration on French data shows that the number of deaths with no lockdown but equilibrium efforts is only 1/6 to 1/10 of the number predicted with business-as-usual. However, lockdown saves at least 50% more lives than individual efforts alone. Prolonged weaker restrictions prevent an exponential rebound. Public policies post-lockdown have a limited impact as they partly crowd out individual efforts. Compulsory mask wearing helps resume activity but has no impact on the epidemic. Communication that increases risk salience is more effective.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
C. A. obtained funding from ANR CHESS grant (grant no. ANR-17-EURE-0010) E. A-V obtained funding from ANR flash COVID-19 (grant MPCUII).
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Not applicable. No patient/participation.
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Data Availability
All data use is publicly available from the French national health agency. https://www.data.gouv.fr/en/datasets/donnees-hospitalieres-relatives-a-lepidemie-de-covid-19-en-france/