Forecasting COVID-19 and Analyzing the Effect of Government Interventions

Abstract Background During the COVID-19 epidemic, governments around the world have implemented unprecedented non-pharmaceutical measures to control its spread. As these measures carry significant economic and humanitarian cost, it is an important topic to investigate the efficacy of different policies and accurately project the future spread under such said policies. Methods We developed a novel epidemiological model, DELPHI, based on the established SEIR model, that explicitly captures government interventions, underdetection, and many other realistic effects. We estimate key biological parameters using a meta-analysis of over 190 COVID-19 research papers and fit DELPHI to over 167 geographical areas since early April. We extract the inferred government intervention effect from DELPHI. Findings Our epidemiological model recorded 6% and 11% two-week out-of-sample Median Absolute Percentage Error on cases and deaths, and successfully predicted the severity of epidemics in many areas (including US, UK and Russia) months before it happened. Using the extracted government response, we find mass gathering restrictions and school closings on average reduced infection rates the most, at 29.9 ± 6.9% and 17.3 ± 6.7%, respectively. The most stringent policy, stay-at-home, on average reduced the infection rate by 74.4 ± 3.7% from baseline across countries that implemented it. We also further show that a reversal of stay-at-home policies in some countries, such as Brazil, could have disastrous results by end of July. Interpretation Our findings highlight that among the widely implemented policies around the world, mass gathering restrictions and school closings appear to be the most effective policies in reducing the infection rate. Given the continued spread of the epidemic in many countries, we recommend these policies to continue to the extent that they can be feasibly implemented. Our results also show that under an assumption of R0 of 2.5-3 for COVID-19, stay-at-home policies appear to be the only effective policy that was widely implemented in reducing the R0 below 1. This implies that stay-at-home policies might be necessary, for at least the vulnerable population, if an uncontrolled second wave reemerges. Research in Context Evidence before this study Previous research into COVID-19 has focused on reporting estimates of epidemiological parameters of COVID-19. We conducted an extensive literature search on PubMed and MedRXiv including keywords such as “non-pharmaceutical interventions” and “government interventions”. We discovered some studies reporting on the theoretical effect of non-pharmaceutical interventions in a theoretical modeling framework. There have also been a few published studies reporting on the overall effect of government interventions in the very early stages of the epidemics in various regions, such as the United States and Europe. However, there were few studies that tried to quantify the effect of each policy that was implemented, and none that the authors know of that are conducted on the global scale of this paper. Added value of this study As governments continue to implement non-pharmaceutical interventions, we aim to understand the effect of different policies that have been implemented in the past. We developed a novel epidemiological model that has been continuously providing high accuracy forecasts since early April. It also provides global estimates for the effects of different policies as they have been implemented across 167 areas. The large number of areas we consider enable us to derive inference for many popular policies that have been implemented, including mass gathering restrictions, school closures, along with travel and work restrictions. Implications of all the available evidence The evidence indicates that mass gathering restrictions were the most effective single policy in reducing the spread of COVID-19, followed by school closings. Stay-at-home policies greatly reduced the effective R0 and most likely enabled the effective control of the epidemics in many regions. Policy simulations suggest that many countries around the world are not yet suitable for a loosening of policy guidance, or there would be potentially severe humanitarian costs.