Is Curfew Effective in Limiting SARS-CoV-2 Progression? An Evaluation in France Based on Epidemiokinetic Analyses

BACKGROUND: Since late summer 2020, the French authorities implemented a curfew/lightened lockdown-alternating strategy instead of strict lockdown, to improve acceptability and limit socioeconomic consequences. However, data on curfew-related efficacy to control the epidemic are scarce. OBJECTIVE: To investigate the effects on COVID-19 spread in France of curfew combined to local and/or nationwide restrictions from late summer 2020 to mid-February 2021. DESIGN: We conducted a comparative evaluation using a susceptible-infected-recovered (SIR)–based model completed with epidemiokinetic tools. MAIN MEASURES: We analyzed the time-course of epidemic progression rate under curfew in French Guyana and five metropolitan regions where additional restrictions were implemented at different times. Using linear regressions of the decay/increase rates in daily contaminations, we calculated the epidemic regression half-lives (t(1/2β)) for each identified period. KEY RESULTS: In French Guyana, two decay periods with rapid regression (t(1/2β) of ~10 days) were observed under curfew, with slowing (t(1/2β) of ~43 days) when curfew was lightened. During the 2-week pre-lockdown curfew (2020/10/17–2020/11/02) in Provence-Alpes-Côte-d’Azur, Auvergne-Rhône-Alpes, and Ile-de-France, the epidemic progression was unchanged. During the post-lockdown curfew (2020/12/15–2020/02/14), the epidemic slowly regressed in Grand-Est (t(1/2β) of ~37 days), whereas its progression rate plateaued in Auvergne-Rhône-Alpes and increased immediately in Provence-Alpes-Côte-d’Azur, Ile-de-France, and Nouvelle-Aquitaine, whatever the curfew starting time was (06:00 or 08:00 pm). Interestingly, a delayed slow decay (17 days < t(1/2β) < 64 days) occurred under curfew in all regions except Ile-de-France. CONCLUSIONS: Curfew allowed the temporary control of SARS-CoV-2 epidemic, however variably in the French regions, without preventing lockdown necessity. To accelerate the epidemic regression such as observed in French Guyana, curfew should be implemented timely with additional restrictions.