Of all the issues that have roiled ties between China and the West since the pandemic emerged, none has been more sensitive in Beijing than questions about the origin of COVID-19.

China last year responded to U.S. ally Australia’s initial push for an independent probe into where the virus came from with tariffs on exports of its barley and wine. Since then, Beijing has repeatedly blasted calls for more transparency as politically motivated, and sought to deflect suggestions it came from a laboratory in Wuhan with alternative origin theories ranging from transmission via frozen-food imports to a release from U.S. bio-facilities.

That made U.S. President Joe Biden’s revival of the lab theory last week — by giving intelligence agencies 90 days to get closer to a definitive conclusion on the origin of the coronavirus — all the more meaningful. The order came as political pressure increased following a series of reports suggesting the theory, which was prominently backed by Trump administration officials, had been prematurely disregarded. Even Facebook Inc. said it would stop taking down posts claiming COVID-19 was human-made or manufactured.