Following the skyrocketing increase in the number of cases of COVID-19 that demonstrated that it was no longer possible to contain the spread of the disease, the governments of many countries launched mitigation strategies in an attempt to halt the spread of the epidemic and flatten its curve. Only China opted for applying a suppression strategy aimed at reversing the epidemic by reducing the basic reproduction number to less than one. The Spanish Government started to adopt physical distancing measures on 14 March 2020, 13 days after the epidemic outbreak began to exhibit an exponential growth. In most countries, these measures were reversed as of June 2020. In the case of Spain, specifically, the end of lockdown was declared on 21 June 2020.
The purpose of this study was to evaluate the effectiveness of the measures adopted by the Spanish Government to mitigate the COVID-19 epidemic before the flattening of the epidemic curve. Our hypothesis was that the behavior of the epidemic curve has been very similar in all countries. We applied a time series design using information collected between 17 January 2020 and 5 April 2020 on daily new cases of COVID-19 reported in Spain, China, and Italy. In addition, we specified two generalized, linear, mixed models (GLMM) with Gaussian response variables (i.e., linear mixed models): one to explain the shape of the epidemic curve of cumulative cases and the other to estimate the effects of the intervention.
Only one day after implementing the measures, the variation rate of accumulated cases in Spain decreased daily by 3.059 percentage points on average (95% credibility interval: ‑5.371, -0.879). This decrease was greater over time. The reduction in the variation rate of the accumulated cases on the last day for which we had available data (April 5th) reached 5.11 percentage points.
Thus, we concluded that the measures adopted by the Spanish Government on 14 March 2020 to mitigate the COVID-19 pandemic succeeded in flattening the curve and paved the way for its reduction.
During the pandemic, we were one of the first research groups to evaluate the measures implemented to flatten the COVID-19 epidemic curve and to analyze the impact of long‑term exposure to atmospheric pollutants on the spatiotemporal diffusion of COVID‑19 in the particular cases of Spain and Catalonia, respectively.