Impact of Lockdown on COVID-19 Transmissibility During the First Pandemic Wave in Spain

Abstract

Background: The analysis of the evolution of the COVID-19 epidemic can provide evidence of the impact of measures implemented to reduce its progression. Our aim was to describe the evolution of the pandemic in the different Spanish regions and to examine the effect of the non-pharmaceutical public health interventions during the first epidemic wave on these trends. Methods: Daily incidence rates of cases were calculated at national and regional level between 31th of January and 10th of May 2020. Epidemic curves, important dates of interventions and effective reproduction number (Rt) were plotted and transmissibility parameters were calculated. To summarize the geographical heterogeneity in the evolution, regional epidemic curves have been classified into homogeneous groups using a clustering procedure. Findings: The incidence rate reached 5 cases per 100,000 on March 1 and peaked at March 20. The Rt gradually decreased after the national lockdown falling below 1 on March 24. Two homogeneous groups of epidemic curves were identified among regions, mainly differentiated by the magnitude of the daily incidence rate and the evolution of the Rt in the period prior to lockdown. However, irrespectively of the previous trend, the lockdown was followed by a steep decrease in the number of cases starting 6 days after its implementation. Interpretation: Our results confirm that the restrictive national lockdown efficiently reduced the progression of the epidemic in Spain during the first wave. This effect was similar in the two regional clusters, independent of the previous dynamics of the epidemic.