The phylodynamics of SARS-CoV-2 during 2020 in Finland — Disappearance and re-emergence of introduced strains.

Abstract

Finland has had a low incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infections as compared to most European countries. Here we report the origins and turnover of SARS-CoV-2 lineages circulating in Finland in 2020. SARS-CoV-2 introduced to Finland in January 2020 and spread rapidly across southern Finland during spring. We observed rapid turnover among Finnish lineages during this period. Clade 20C became the most prevalent among sequenced cases and was replaced by other strains in fall 2020. Bayesian phylogeographic reconstructions suggested 42 independent introductions into Finland during spring 2020, mainly from Italy, Austria, and Spain, which might have been the source for a third of cases. The investigations of the original introductions of SARS-CoV-2 to Finland during the early stages of the pandemic and of the subsequent lineage dynamics could be utilized to assess the role of transboundary movements and effects of early intervention and public health measures.

Phylodynamic Dispersal of SARS-CoV-2 Lineages Circulating across Polish–German Border Provinces

“…A high proportion of observed singletons suggests that onward transmission of the introduced virus was uncommon despite multiple independent introduction events. The estimates of the relative contribution of external introductions in establishing regional transmission chains in PL-DE Interreg gave similar observations to the one noted in New York State (116 introductions in 828 sampled genomes) [ 46 ] and Finland (42 introductions of 333 genomes) [ 47 ]. Insights from regions sampled at very high densities, such as the United Kingdom, show that the majority of introductions lead to small, transient, dead-end transmission lineages, whereas a small number of introductions lead to larger and longer-lasting transmission lineages [ 38 ].…”