Coronavirus malady: The scientists are still racing to solve the mysteries

They have learnt how the virus enters and hijacks cells, how some people fight it off and how it eventually kills others.by Anwar A.

KhanFrom immunity to the role of genetics, Nature looks at five pressing questions about COVID-19 that researchers are tackling.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 more than 800 people. The COVID-19 pandemic has becomethe worst public-health crisis in a century.

More than 4,000,000people 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 2020.But for every insight into COVID-19, more questions emerge and others linger.

That is how science works. 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.

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 KariStefansson, 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.That search has been hampered by the relatively small number of cases in Iceland.

But an international team analysing the genomes of roughly 4,000 people from Italy and Spain turned up the first strong genetic links to severe COVID-191. People who developed respiratory failure were more likely to carry one of two particular gene variants than were people without the disease.One variant lies in the region of the genome that determines ABO blood type.

The other is near several genes, including one that encodes a protein that interacts with the receptor the virus uses to enter human cells, and two others that...