In late December 2019, reports emerged of a mysterious pneumonia in Wuhan, China, a city of 11 million people in the southeastern province of Hubei. The cause, Chinese scientists quickly determined, was a new coronavirus distantly related to the SARS virus that had emerged in China in 2003, before spreading globally and killing nearly 800 people.
Six months and more than ten million confirmed cases later, the COVID-19 pandemic has become the worst public-health crisis in a century. More than 500,000 people have died worldwide. It has also catalysed a research revolution, as scientists, doctors and other scholars have worked at breakneck speed to understand COVID-19 and the virus that causes it: SARS-CoV-2.
They have learnt how the virus enters and hijacks cells, how some people fight it off and how it eventually kills others. They have identified drugs that benefit the sickest patients, and many more potential treatments are in the works. They have developed nearly 200 potential vaccines — the first of which could be proved effective by the end of the year.
But for every insight into COVID-19, more questions emerge and others linger. That is how science works. To mark six months since the world first learnt about the disease responsible for the pandemic, Nature runs through some of the key questions that researchers still don’t have answers to.
Why do people respond so differently?
One of the most striking aspects of COVID-19 is the stark differences in experiences of the disease. Some people never develop symptoms, whereas others, some apparently healthy, have severe or even fatal pneumonia. “The differences in the clinical outcome are dramatic,” says Kári Stefánsson, a geneticist and chief executive of DeCODE Genetics in Reykjavik, whose team is looking for human gene variants that might explain some of these differences….
