This week a team of international experts from the WHO will arrive in China to investigate the origins of Covid-19. A year into the pandemic, Guardian health editor Sarah Boseley looks at what questions still need to be answered

A World Health Organization team of international experts tasked with investigating the origins Covid-19 will arrive in China this week. Scientists want to determine how the virus jumped species into humans. A year into the pandemic there are still many unanswered questions over the origins of the novel virus.

The Guardian’s health editor, Sarah Boseley, tells Rachel Humpheys about what the WHO has uncovered over the past 12 months and the challenges it has faced. Ideally, door-to-door detective work, talking to the first people to fall ill and their families and colleagues, would have begun in Wuhan in January. But the city was in lockdown, its streets deserted. And the rest of the world had not yet understood what it was facing, Bruce Aylward, the Canadian doctor and epidemiologist appointed by WHO to lead its fact-finding mission to China in early February told Sarah in a recent phone call.