Viral lineages suggest multiple spillovers as origin of the COVID-19 pandemic

Updated: Nov 24, 2021

While several theories suspect the possible escape of the SARS-CoV-2 virus from a research laboratory in China, the preliminary analysis of viral genomes from early in the pandemic disputes this theory and supports the hypothesis that SARS-CoV-2 pathogens might have spread from animals to humans on several occasions, suggesting the pandemic potentially originated from multiple markets in Wuhan, China.

Looking closely into the earliest viral genomes from late 2019 and early 2020, there are two broad viral lineages, known as A and B, with key genetic differences. Lineage B is now the globally dominant lineage which includes samples taken from people visiting the Huanan seafood and wild animal market. Lineage A is mostly limited to within China, known to have originated from other markets in Wuhan.

The two viral lineages do not seem to be evolving from one another with clearly defined origins, suggesting the possibility of multiple spillover events. Since it requires at least two spillover events for a researcher to accidentally get infected in the lab and potentially spread the virus to the population at large, it is less likely that it leaked from a lab and much more likely the COVID-19 pandemic originated in the wildlife trade.

The team of researchers performing this latest analysis plans to conduct further tests on how well multiple spillovers would fit with the diversity of known SARS-CoV-2 genomes, providing us with additional evidence to support this hypothesis. Read more about their current findings here.