Coronavirus is spreading like wildfire. Just four months after it was first detected, it has spread to over 180 countries, infecting more than 1 million people.

At this moment, at least 20 vaccines are in development around the globe. But there is still so much we don't know about the virus – how it spreads, how it affects its victims. 

The following cases shed light on why we should remain cautious about this slowly unraveling mystery.

On-camera reporter: Serena Dong

Scriptwriter: Serena Dong

Video editor: Zhang Wanbo

Filmed by Fu Gaoliang

Chief editor: Wang Xin

Producer: Wen Yaru

Director: Zhang Shilei

Supervisor: Fan Yun