The goal of the series is to provide a platform for rapid communication and exchange of ideas concerning the COVID-19 epidemic. It is new and unlike the known virus-induced diseases. There is a significant research effort, including mathematical modelling, to understand the characteristics of the virus SARS-CoV-2 and the epidemiological dynamics of COVID-19, the disease caused by it. Due to their novelty, the research is often likely to produce results only on specific aspects of the disease, provide just partial answers to research questions, or collect evidence for formulating hypothesis yet to be tested. We believe, however, that the significance of the pandemic for the human population makes it essential to share even such partial results as soon as they are available to facilitate the advancement of the research on this disease. While eventually, a more comprehensive picture of both the virus and the disease will emerge, even incomplete but timely and scientifically-based information will help the authorities to make sound decisions on the course of action during the epidemic. For the series, we invite publications on any aspect of the COVID-19 epidemic. Specifically, the series aims to cover the biological research, providing an understanding of the relevant structures and causal relationships in the epidemiological environment, which can facilitate mathematical or statistical modelling, mathematical models of the structures, causal interactions and epidemiological data, and their analysis, mathematical models and analysis of the socio-economic aspects of the pandemic,· any new mathematical methods, applicable to the study of any of the mentioned topics.