For almost two years, COVID-19 has been spreading to and in virtually all "corners" of the world. A first wave in early 2020 saw cases being detected in the immense majority of national level jurisdictions in a little over three months after the start of spread. Subsequent waves involving novel variants of SARS-CoV-2 then occurred starting late 2020 and have been ongoing since. These waves are illustrative of the heterogeneity of transmission activity that has characterised the spatio-temporal spread of COVID-19: not all locations were affected by the same variants at the same time and in the same manner. Heterogeneity has also been observed, for locations exhibiting the same variant distribution, at the local level: some jurisdictions experienced sustained transmission chains, while others, for instance in Maritime Canada, mostly saw importation-driven short chains resulting in intermittent population-level spread. Various measures introduced to curtail COVID-19's spatio-temporal spread have also had varied levels of success.

Understanding the drivers of spread and importation, the role of measures used to control these processes and, most importantly, the causes of observed heterogeneities, is therefore of crucial importance not only in the fight against COVID-19 but also in anticipation of future pandemics. In this presentation, I will discuss issues related to the spatial and temporal spread of COVID-19. Most of the talk will be devoted to a data-based investigation of the topic, but I will also present some modelling approaches that were used to study these issues and highlight what I believe are the main open questions facing public health professionals and modellers interested in the spatio-temporal spread of infectious pathogens.