Swiss public health measures associated with reduced SARS-CoV-2 transmission using genome data

Genome sequences allow quantification of changes in case introductions from abroad and local transmission dynamics. We sequenced 11,357 SARS-CoV-2 genomes from Switzerland in 2020 - the 6th largest effort globally. Using these data, we estimated introductions and their persistence throughout 2020. By contrasting estimates with null models, we estimate at least 83% of introductions were adverted during Switzerland9s border closures. Further, transmission chain persistence roughly doubled after the partial lockdown was lifted. Then, using a novel phylodynamic method, we suggest transmission in newly introduced outbreaks slowed 36 - 64% upon outbreak detection in summer 2020, but not in fall. This could indicate successful contact tracing over summer before overburdening in fall. The study highlights the added value of genome sequencing data for understanding transmission dynamics.