Impact of national lockdown in reducing SARS-CoV-2 transmission in Portuguese municipalities

Background: Rapid spread of the SARS-CoV-2 infections was responsible for the rupture of health services and forced drastic lockdown measures in many countries, driving millions into a socioeconomic crisis. Understanding the impact of non- pharmacological interventions on epidemic control in different socioeconomic contexts is important to inform decision-makers. We aimed to compare the effect of nationwide lockdown on SARS-Cov-2 incidence in different municipalities, grouped by socioeconomic features. Methods : Based on national surveillance data on a laboratory confirmed SARSCoV- 2 cases we developed an ecological interrupted time series analysis study in 277 Portuguese municipalities grouped by socioeconomic features using two- steps cluster analysis. Change in SARS-COV-2 daily incidence after lockdown introduction on March 18, 2020 was estimated in each cluster by negative binomial regression. Two municipality clusters were considered, with cluster A characterized by younger population with lower education and purchasing power and smaller population density. Results: Before lockdown, incidence rates increased by 24,7% and 19,0% daily, reaching 11,42 and 14,11 per 100.000 inhabitants in cluster A and B, respectively. With lockdown introduction, rates decreased by 4,0% and 4,2% daily, reaching 2,96 and 3,50 per 100.000, in cluster A and B 42 days after restrictions implementation. Overall, lockdown measures avoided 138.676,76 and 60.404,15 cases per 100.000, in cluster A and B, respectively. Conclusions: Before lockdown, higher SARS-CoV-2 transmission was observed in the municipalities with lower socioeconomic status, which was expected, considering these socioeconomic features are associated with higher transmission of the virus. Lockdown prevented more cases in these municipalities. Despite the socioeconomic impact, lockdown has demonstrated to be a crucial measure to control SARS-CoV-2 transmission, particularly in municipalities with lower socioeconomic status.N/