ABSTRACT
Molecular epidemiology has provided an additive value to traditional public health tools by identifying SARS-CoV-2 clusters, or providing evidence that clusters based on virus sequences and contact tracing are highly concordant. Our aim was to infer the levels of virus importation and to estimate the impact of public health measures related to travel restrictions to local transmission in Greece. Our phylogenetic and phylogeographic analyses included 389 SARS-CoV-2 sequences collected during the first 7 months of the pandemic in Greece and a random collection in 5 replicates of 3,000 sequences sampled globally, as well as the best hits to our dataset identified by BLAST. Phylogenetic analyses revealed the presence of 70 genetically distinct viruses identified as independent introductions into Greece. The proportion of imported strains was 41%, 11.5%, and 8.8% during the three periods of sampling, namely, March (no travel restrictions), April to June (strict travel restrictions), and July to September (lifting of travel restrictions based on a thorough risk assessment), respectively. These findings reveal low levels of onward transmission from imported cases during summer and underscore the importance of targeted public health measures that can increase the safety of international travel during a pandemic.
ABSTRACT
SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is a novel Coronavirus responsible for the Coronavirus Disease-2019 (COVID-19) pandemic. Since the beginning of the pandemic, the virus has spread in almost the entire world. Tracing and tracking virus international and local transmission has been an enormous challenge. Chains of infections starting from various countries worldwide seeded the outbreak of COVID-19 in Athens, capital city of Greece. Full-genome analysis of isolates from Athens Hospitals and other healthcare providers revealed the variety of SARS-CoV-2 that initiated the pandemic before lock-down and passenger flight restrictions. The present work may serve as reference for resolving future lines of infection in the area and Europe especially after resumption of passenger flight connections to Athens and Greece during summer of 2020.
