A huge amount has emerged about the new virus already, but many vital of the details needed to control the outbreak remain unknown.
At the end of December, Chinese authorities put out a public warning that a “pneumonia of unknown cause” had been identified in Wuhan.
Roughly 10 days later, scientists identified a new coronavirus as the source of the outbreak, but said the disease did not appear to be spreading between humans.
Fast forward three weeks and the virus – currently known as 2019-nCoV – has infected more than 9,600 people, killed 213 and spread to some 20 other countries.
A remarkable amount of information about the virus has been unearthed in record time – including its full genetic code – but there remain vital unanswered questions.
Here is an overview of the questions keeping scientists across the globe awake at night. Their answers will determine the course of the outbreak in the weeks and months to come.
How infectious is the coronavirus?
We know now the disease is spread between people and that respiratory droplets – spittle and mucus – are the the key drivers for it’s spread.
But that’s only a start. Experts are especially worried about research published in The Lancet suggesting people can carry and spread the virus even if they are not showing symptoms.
“We know silent infections exist, but we have no idea how widespread they are,” said Jonathan Ball, professor of molecular virology at the University of Nottingham.
“If it’s just a minority of asymptomatic cases that can transmit the coronavirus to a few other people, the contribution to the overall outbreak is very small and it’s much less worrying.”
With severe acute respiratory syndrome (Sars), patients were most likely to infect other people at the height of their own illness, when they were displaying a high fever. This meant you could isolate them and stop onward transmission – Ebola is similar.
With 2019-nCoV, the same does not seem to apply. In Germany, a case was confirmed in a man with no travel history to China, but who came into contact with a colleague visiting from Shanghai. This colleague did not develop symptoms until she got back home, but by this point had already passed the infection on.
“If what we’ve seen in Germany plays out elsewhere, that has huge implications for infection control,” said Jeremy Konyndyk, a senior fellow at the center for global development and former Obama-era director of the Office of US Foreign Disaster Assistance. “How can you even begin to isolate people showing no symptoms?
Over the last few days research has emerged estimating the incubation period, speed of spread and most vulnerable groups. The most comprehensive paper, published in the New England Journal of Medicine by the Chinese Centre for Disease Control and Prevention in Beijing, suggests that the virus has a mean incubation period of 5.2 days.
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The study added that the total number of cases at the outset were doubling every seven days, and there were no children under 15 were infected out of the 425 cases they looked at.
“Our preliminary estimate for the incubation period distribution provides important evidence to support a 14-day medical observation period or quarantine for exposed persons,” the researchers said.
How dangerous is the disease?
It appears that 2019-nCov triggers a wide spectrum of illness, from mild to severe, but it’s unclear how many of the mild infections have been identified.
“The really big question is just how widespread this is, the scale of it,” said Prof Ball. “In an outbreak, we tend to focus on the most extreme cases to start with – these are the people who require urgent care.”
But until we have a full picture, it’s almost impossible to accurately do the maths and work out how dangerous the disease is, added Prof Ball.
According to research published in The Lancet, 75,800 people in Wuhan alone could have been infected with the new virus as of 25 January – the authors note that the figure is probably far higher than official numbers because “not everyone who is infected with 2019-nCoV would require or seek medical attention.”
China’s national health authorities said this week that three per cent of patients with the virus died and 17 per cent were “severely” ill – a figure the WHO put at 20 per cent. But these figures could drop significantly if many more mild cases were confirmed.
Mr Konyndky said: “If we find that this disease manifests in a lot of people but is mild, that’s actually a good thing, it means it’s far less dangerous that it might seem right now.”
On the other hand, in countries less than developed than China, death rates could rise because “severe” cases may not have access to the hospitalisation they require.
How far has the coronavirus spread?
Another huge unknown is where exactly the coronavirus is. Although the world is on high alert, it is notable that the countries which have so far confirmed cases all have well resourced health systems with an advanced disease surveillance infrastructure.
“If the virus is introduced into low and middle income countries (LMIC), areas without as many resources, then firstly there might be a delay in identifying it,” said Prof Ball. “But secondly, these are very often the places that are most highly populated.”
Experts say it is likely that the virus will reach countries in Africa given that China has invested billions in the continent in the last decade, predominantly via the Belt and Road Initiative. Cases are already being investigated in Kenya, Ethiopia and the Ivory Coast.
“My default assumption is that it will reach Africa – it probably already has – given the high volume of travel between the continent and China,” said Mr Konyndky.
“That’s really concerning – infection control weak is in a lot of places, but it’s particularly bad and under resourced in some of the weaker health systems in Africa.”
There is also concern that some regions of Asia could be unprepared for 2019-nCov – both in terms of identifying it and responding to cases. Although an infection has been confirmed in India, for example, commentators are worried this could just be the tip of the iceberg.
“Past experience shows that most hospitals in India and other low to middle income countries may not be prepared for the surge capacity of patients with infectious diseases like coronavirus,” said Dr Jyoti Joshi, the head of the Center for Disease Dynamics, Economics and Policy.
On overall numbers, experts at Imperial College, London estimate there are at least 100,000 cases in China alone already. Worldwide the number could be higher still.
Do counter measures work?
The WHO has praised China’s strong response to the coronavirus outbreak, in sharp contrast to the country’s handling of the Sars epidemic in 2002-2003.
China has introduced quarantines (now affecting more than 50 million people), built new hospitals from scratch, and shut down transport links.
“The fact that to date we have only seen 68 cases outside China, and no deaths, is due in no small part to the extraordinary steps the government has taken to prevent the export of cases,” Dr Tedros Adhanom Ghebreyesus, director general of the WHO, told a press conference on Wednesday.
“For that, China deserves our gratitude and respect. They’re doing that at the expense of their economy,” he said.
But while some have criticised China’s quarantines as draconian – saying it could push cases underground – others are worried about whether it was too late. Millions of people had already left Wuhan amid Lunar New Year celebrations before the shutdown was enforced.
“We can probably expect that this is not going to contain the outbreak, we are beyond that point already,” said Mr Konyndyk. “But I do think it’s plausible that the quarantine temporarily decelerated the spread.
“There was concern that a huge mass migration event for Chinese New Year would significantly increase infections across China, and I think the quarantine has forestalled that.”
There is also evidence emerging that airport screenings are not as effective as hoped – a team at the LSHTM have found that almost two-thirds of airport screening tests have failed to detect the coronavirus.
What is the R0 number?
One measure experts use to try and get a handle on transmissibility is the R0 number. It’s not an indication of how dangerous the disease is, but is used to determine the potential for a virus to rapidly spread. The higher the R0 number, the more infectious an illness is.
“Various things impact that R0 value,” said Prof Ball. “The susceptibility, size and density of the population that the infection is introduced into, and then also the infectiousness of the virus itself.
“The reason we’re interested is not only does it give you an idea of how many people the virus is likely to infect, it also gives you an idea of how effective your interventions need to be.”
But it’s incredibly difficult to identify the R0 number at the onset of an outbreak – especially when it is unclear how many people have been infected.
