A preliminary analysis of viral genomes suggests the COVID-19 pandemic might have multiple animal origins — but the findings still have to be peer reviewed.

By Smriti Mallapaty

SARS-CoV-2, the virus that causes COVID-19, could have spilled from animals to people multiple times, according to a preliminary analysis of viral genomes sampled from people infected in China and elsewhere early in the pandemic.

If confirmed by further analyses, the findings would add weight to the hypothesis that the pandemic originated in multiple markets in Wuhan, and make the hypothesis that SARS-COV-2 escaped from a laboratory less likely, say some researchers. But the data need to be verified, and the analysis has not yet been peer reviewed.

The earliest viral sequences, taken from people infected in late 2019 and early 2020, are split into two broad lineages, known as A and B, which have key genetic differences.

Lineage B has become the dominant lineage globally and includes samples taken from people who visited the Huanan seafood market in Wuhan, which also sold wild animals. Lineage A spread within China, and includes samples from people linked to other markets in Wuhan.

A crucial question is how the two viral lineages are related. If viruses in lineage A evolved from those in lineage B, or vice versa, that would suggest that the progenitor of the virus jumped just once from animals to people. But if the two lineages have separate origins, then there might have been multiple spillover events.

Dagger in the heart

The latest analysis — posted on the virological.org discussion forum — adds weight to the second possibility by questioning the existence of genomes linking the lineages.

The finding could be the “dagger into the heart” of the hypothesis that SARS-CoV-2 escaped from a lab, rather than originating from the wildlife trade, says Robert Garry, a virologist at Tulane University in New Orleans, Louisiana. But others say that more research is needed, especially given the limited genomic data from early in the pandemic.

“It is a very significant study,” says Garry. “If you can show that A and B are two separate lineages and there were two spillovers, it all but eliminates the idea that it came from a lab.”

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