Abstract
BACKGROUND: The spread of SARS-CoV-2 has been influenced by multiple factors, from the inherent transmission capabilities of the different variants to the control measurements put in place. Understanding how new variants enter a country is essential for managing future outbreaks. This study investigates how three major variants-Alpha, Delta, and Omicron (BA.1)-entered Spain and how different restrictions potentially affected their introduction. METHODS: We collected Spanish and international SARS-CoV-2 genomes from the GISAID database. Leveraging connectivity data from different countries with Spain, we performed a phylodynamic Bayesian analysis of the SARS-CoV-2 introductions into Spain. RESULTS: Most introductions of the Alpha variant originated from France. As travel restrictions eased, the number of introductions from different countries increased. During the Delta and Omicron waves, the United Kingdom and Germany became important sources of the virus. The highest number of introductions occurred during the Delta wave, coinciding with fewer travel restrictions and the summer season, when Spain receives a considerable number of tourists. CONCLUSIONS: Our findings highlight the role of international travel in the spread of new variants. They underscore the importance of monitoring travel patterns and implementing targeted public health measures to manage the spread of SARS-CoV-2.