Coronasurveys: indirect online surveys to monitor the evolution of COVID-19

Introduction: Monitoring the evolution of COVID-19 has been essential for health decision-making. But this requires reliable numbers of the infected, dead and hospitalized, often difficult to have for multiple reasons. The use of fast and reliable estimation techniques, such as indirect surveys, is an option. Objectives: To present the CoronaSurveys project, which monitors COVID-19 by combining indirect surveys with the Network Scaleup Method (NSUM). Methodology: The system uses indirect online anonymous surveys to inquire about COVID-19, and the NSUM method to estimate cases. The system offers multi-language surveys with questions to track active cases, new cases, and fatalities, among others. Results: CoronaSurveys has been operating since March 2020, and continues to collect data, with over one hundred responses to date (over one million samples). The system has made good estimates for Spain and the United Kingdom, among other countries. Conclusion: This system is suitable in countries with limited health infrastructure or in situations of lack of knowledge about the pandemic, such as at the beginning of COVID-19, because its implementation cost is small and it requires simple devices to use it and few participants to obtain good estimates.