Phylogenetic insights into the early spread of the SARS-CoV-2 Alpha variant across Europe

The evolution of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has profoundly influenced the trajectory of the COVID-19 pandemic. In late 2020, the Alpha variant (Pango lineage B.1.1.7) emerged in South East England, characterized by enhanced transmissibility, increased mortality, and rapid geographic expansion. Here, we studied the evolutionary history and migration dynamics of Alpha across Europe using genomic data sourced from 38 European countries. Our findings reveal that Alpha was introduced to over 25 European countries within 90 days of its emergence, with the UK accounting for 61% of early exportation events. However, as the epidemic progressed, several mainland European countries, including France, Denmark, and the Czech Republic, became significant hubs of onward transmission. Social mixing during the December holiday period and air travel facilitated the variant's rapid dissemination, as corroborated by air passenger flight volumes and viral introductions. Notably, genomic surveillance intensified after Alpha was designated a variant of concern, reducing the detection lag in countries with later introductions. Our study highlights the critical interplay between international mobility, surveillance efforts, and regional connectivity in shaping the epidemiology of SARS-CoV-2 variants and underscores the need for coordinated genomic surveillance and timely interventions to mitigate the spread of emerging pathogens.