Capturing the spatiotemporal spread of COVID-19 in 30 European countries during 2020 - 2022.

BACKGROUND: While the COVID-19 pandemic has been burdensome globally, it has fostered extensive data collection at various spatiotemporal resolutions. These data heightened researchers' interest in investigating multiple facets of the pandemic. In Europe, key factors shaping disease transmission vary among countries, leading to a gap in understanding how the epidemic evolved and spread across countries as a whole. We endeavor to understand the similarities and differences in the spatiotemporal spread of the COVID-19 pandemic across 27 European Union (EU) countries and 3 European Economic Area (EEA) countries between March 2020 and December 2022. METHOD: We utilized a multivariate endemic-epidemic model to conduct a space-time analysis across 30 countries, using weekly aggregated COVID-19 case counts from week 13-2020 to week 50-2022. Our analysis considered the discrepancies in population size, the primary course and three booster vaccine doses - taking into account waning immunity, the Stringency Index as a surrogate for non-pharmaceutical interventions adopted in each country, and the circulation of various viral variants. We employed a power law approximation for spatial interactions between countries. RESULTS: We found that within-country transmission was dominant across all countries over almost three years of observation. This work also underscored a basic transmission mechanism, whereby infections introduced by between-country transmission could be of great importance in subsequent local transmission. Furthermore, there were indications of the transition to endemicity since the beginning of 2022, particularly in light of the evolving variants of concern. CONCLUSION: Our study highlighted the benefit of the endemic-epidemic framework to elucidate the COVID-19 disease spread over a large spatial and temporal scale, using a wide range of epidemiological information. Insights derived from this study are beneficial for those interested in seeking an overview of the emergency phase of the COVID-19 pandemic in the EU/EEA region.