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Public Health Steps Slowed SARS-CoV-2 Transmission in Switzerland

Public health measures taken in Switzerland in 2020 slowed SARS-CoV-2 transmission, according to a new genomic sequencing-based analysis. Researchers led by ETH Zurich's Tanja Stadler sequenced more than 11,000 SARS-CoV-2 genomes isolated in Switzerland that year and, using that data in combination with data for some non-Swiss samples from GISAID, constructed phylogenies. Based on these, they modeled viral introductions into Switzerland and viral transmission dynamics in relation to public health measures the Swiss took, including contact tracing, lockdowns, and border closures. As they report in Science Translational Medicine, the researchers found that the spring 2020 partial location and the partial border closure periods led to a reduction in the number of COVID-19 cases imported into Switzerland as well as to a decline in local viral transmission. In particular, they estimate a between 86 percent to 98 percent reduction in viral introductions when Switzerland had its strictest border closures. The researchers also note a decline in viral transmission during the summer, which they say could be due to a more successful contact tracing effort then, though that effort was then overwhelmed in the fall. "The study highlights the added value of genome sequencing data for understanding transmission dynamics," the researchers write.