Superspreader Events Provide New Insights into SARS-CoV-2

A recent study has provided new and deep insights into the current coronavirus disease 2019 (COVID-19) pandemic. The research analyzed epidemiological data from early Superspreader events during the first wave of COVID-19 in Austria.

The study, published in Science Translational Medicine, was conducted by a research group at the CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences. The focus of the research was to gain a more thorough understanding of the SARS-CoV-2 virus and how its mutational dynamics and transmission properties allow it to spread so rapidly.

The project was called “Mutational dynamics of SARS-CoV-2 in Austria”, and made use of the country’s well-developed epidemiological surveillance system and its high-quality data. Austria’s healthcare system has conducted contact tracing on all of its 21,821 reported SARS-CoV-2 cases. This allowed the group of researchers to reconstruct many major infection clusters, analyzing their roles in the spread of the virus internationally. The data also allowed them to analyze genome sequencing from family clusters and transmission chains, determining genetic bottlenecks and the mutation dynamics of the COVID-19 virus.

Demonstrated through the study was how emerging low-frequency mutations of SARS-CoV-2 had become fixed in local clusters. These local clusters were followed by the virus spreading across countries, where viral mutational dynamics within individuals and across populations connected. This shows that the dynamics of superspreader events are driven by the amount of inter-individual exposures, as well as the quantity of transmitted viruses across time.

One cluster, which consisted of 76 confirmed cases, was reconstructed based on the epidemiological data provided and uncovered an obscure link between two clusters, illuminating a previously unknown relationship. "This example illustrates how contact tracing and virus mutation analysis together provide a strong pillar of modern pandemic control," Andreas Bergthaler, who lead the project said.

It was shown from the research that, on average, 1000 infectious virus particles are passed on from an infected person to a non-infected person, which is much higher in comparison to other infectious viruses like HIV. This finding raises important questions, including if reducing an infected person’s viral load through various measures like mask wearing and social distancing, could prevent the spread of the virus.

"Thanks to excellent epidemiological and our deep virus sequencing data, we could follow how the SARS-CoV-2 virus mutated in one individual and was then transmitted to others," Bergthaler said. The results of the study support other current research projects that are aiming to better understand the pandemic and how to control it.