Despite extensive study by doctors and scientists across the world since the new coronavirus first appeared in China three months ago, much about the virus is still unclear.
Here are five key questions that remain unanswered about the virus officially known as SARS-CoV-2 that leads to Covid-19. Why is it serious for only some? One of the biggest mysteries is why the virus produces few or no symptoms in around 80% of people, according to the World Health Organization, yet in others it can lead to fatal pneumonia. "Findings from February indicated that the clinical spectrum of this disease can be very heterogeneous," said Professor Leo Poon from the School of Public Health at Hong Kong University.