A year and a half into the pandemic, we still do not know exactly where the SARS-CoV-2 virus, which causes COVID-19, came from.

The prevailing view so far has been that the virus “spilled over” from bats into humans. But there are increasing calls to investigate the possibility that it emerged from a lab in Wuhan, China, where Covid first appeared at the end of 2019.

So what do we know for sure, and what do we need still to find out?

We know the sequence of the SARS-CoV-2 virus is close to that of bat coronaviruses. Several decades ago its “ancestor” was circulating in bat populations in southern Asia.