Assessment of COVID-19 intervention strategies in the Nordic countries using genomic epidemiology

ABSTRACT

We explored how the duration, size and number of virus transmission clusters, defined as country-specific monophyletic groups in a SARS-CoV-2 phylogenetic tree, differed between the Nordic countries of Norway, Sweden, Denmark, Finland and Iceland. Our results suggest that although geographical connectivity, population density and openness influence the spread and the size of SARS-CoV-2 transmission clusters, the differing country-specific intervention strategies had the largest impact. We also found a significant positive association between the size and duration of transmission clusters in the Nordic countries, suggesting that the rapid deployment of contact tracing is a key response measure in reducing virus transmission.