This paper describes how mobile phone data can guide government and public
health authorities in determining the best course of action to control the
COVID-19 pandemic and in assessing the effectiveness of control measures such
as physical distancing. It identifies key gaps and reasons why this kind of
data is only scarcely used, although their value in similar epidemics has
proven in a number of use cases. It presents ways to overcome these gaps and
key recommendations for urgent action, most notably the establishment of mixed
expert groups on national and regional level, and the inclusion and support of
governments and public authorities early on. It is authored by a group of
experienced data scientists, epidemiologists, demographers and representatives
of mobile network operators who jointly put their work at the service of the
global effort to combat the COVID-19 pandemic.