China is making it harder to solve the mystery of how Covid-19 began

China has effectively snuffed out Covid-19, thanks to stringent border curbs, mass testing and a surveillance network that allows infected people and their contacts to be tracked via mobile phone

In the year since seafood hawkers started appearing at Wuhan’s hospitals sickened with a strange and debilitating pneumonia, the world has learned a lot about Covid-19, from the way it spreads to how to inoculate against the infection. Despite these advances, a chasm remains in our understanding of the virus that’s killed nearly 2 million people and whipsawed the global economy: we still don’t know how it began.

Where the pathogen first emerged and how it transmitted to humans is a stubborn mystery, one that’s becoming more elusive with each passing month. Before the initial cluster among stall-holders at a produce