A repeat pattern of founder events for SARS-CoV-2 variants in Alaska (preprint)

Alaska is a unique US state because of its large size, geographically disparate population density, and physical distance from the contiguous United States. Here, we describe a pattern of SARS-CoV-2 variant emergence across Alaska reflective of these differences. Using genomic data, we found that in Alaska the Omicron sublineage BA.2.3 overtook BA.1.1 by the week of 2022-02-27, reaching 48.5% of sequenced cases. On the contrary in the contiguous United States, BA.1.1 dominated cases for longer, eventually being displaced by BA.2 sublineages other than BA.2.3. BA.2.3 only reached a prevalence of 10.9% in the contiguous United States. Using phylogenetics, we found evidence of potential origins of the two major clades of BA.2.3 in Alaska and with logistic regression estimated how it emerged and spread throughout the state. The combined evidence is suggestive of founder events in Alaska and is reflective of how Alaskas unique dynamics influence the emergence of SARS-CoV-2 variants.

Founder effect contributes to the unique pattern of SARS-CoV-2 variant B.1.1.519 emergence in Alaska (preprint)

Alaska is the largest geographic state in the United States with the lowest population density and a mix of urban centers and isolated rural communities. The differences in population dynamics in Alaska from the contiguous United States may have contributed to a unique pattern of emergence and spread of SARS-CoV-2 variants observed in early 2021. Here we examined 2,323 virus genomes from Alaska and 278,635 virus genomes from the contiguous United States collected between the first week of December 2020 through the last week of June 2021. We focused on this timeframe because of the notable emergence and spread of the SARS-CoV-2 lineage B.1.1.519 observed in Alaska. We found that this variant was consistently detected in Alaska from the end of January through June of 2021 with a peak prevalence in April of 77.9% unlike the rest of the United States with a peak prevalence of 4.6%. In Alaska, the earlier emergence of B.1.1.519 coincided with a later peak of Alpha (B.1.1.7) when compared to the rest of the United States. We also observed differences in the composition of lineages and variants over time between the two most populated regions of Alaska. Although there was a modest increase in COVID-19 cases during the peak incidence of B.1.1.519, it is difficult to disentangle how social dynamics conflated changes in COVID-19 during this time. We suggest that the viral characteristics, such as amino acid substitutions in the spike protein, and a founder effect likely contributed to the unique spread of B.1.1.519 in Alaska.