Dispersal patterns and influence of air travel during the global expansion of SARS-CoV-2 variants of concern
During 2020 and 2021, the Alpha, Beta, and Gamma variants of SARS-CoV-2, known as variants of concern (VOCs), were widespread worldwide, leading to waves of infections. Subsequently, the Delta variant emerged during a global third wave in 2021, displacing the previous VOCs. In late 2021, the Omicron variant took over, further replacing the Delta variant.
This research employed phylogenetic and phylogeographic methods to analyse the dispersal patterns of these VOCs across the globe. Their findings reveal significant variations in source-sink dynamics for each variant and identify certain countries that acted as crucial hubs for their dissemination on both global and regional scales.
Interestingly, the study demonstrates a declining role of the presumed origin countries in the global spread of VOCs. Specifically,it estimates that India contributed less than 15% of Delta exports, and South Africa only accounted for 1% to 2% of Omicron dispersal.
Notably, within just 100 days of its emergence, Omicron had reached over 80 countries, facilitated by increased passenger air travel and its higher transmissibility. These results underscore the rapid dissemination of highly transmissible variants and emphasise the importance of genomic surveillance within the hierarchical airline network.