A pandemic momentum index to manage the spread of COVID-19

Quantifying the spreading power of a pandemic like COVID-19 is important for the early implementation of early restrictions on social mobility and other interventions to slow its spread. This work aims to quantify the power of spread, defining a new indicator, the pandemic momentum index. It is based on the analogy between the kinematics of disease spread and the kinematics of a solid in Newtonian mechanics. This index, $I_{\mathrm{PM}}$ , is useful for assessing the risk of spread. Based on the evolution of the pandemic in Spain, a decision-making scheme is proposed that allows early responses to the spread and decreases the incidence of the disease. This index has been calculated retrospectively for the pandemic in Spain, and a counterfactual analysis shows that if the decision-making scheme had been used as a guide, the most significant decisions on restrictions would have been advanced: the total number of confirmed cases of COVID-19 would have been much lower during the period studied, with a significant reduction in the total number of cases: 83 % (sd = 2.6). The results of this paper are consistent with the numerous studies on the pandemic that concluded that the early implementation of restrictions is more important than their severity. Early response slows the spread of the pandemic by applying less severe mobility restrictions, reducing the number of cases and deaths, and doing less damage to the economy.