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 But the data need to be verified, and the analysis has not yet been peer reviewed.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.