The new virus belongs to the coronavirus family ALFRED PASIEKA/SCIENCE PHOTO LIBRARY

A deadly new coronavirus has now reached at least 13 countries. As of Monday 27 January, there are 2794 confirmed cases of the virus, while tens of thousands of people are being kept under medical supervision around the world. Eighty-one people have died with the virus, according to latest reports.

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More deaths are predicted to follow. The virus can spread before symptoms show, China’s health minister Ma Xiaowei said on Sunday, which means it will be more difficult to limit transmission between people.

There are confirmed cases of the virus across Asia, and in the US, Australia and Europe. So far, all cases outside China seem to be in people who have travelled from Hubei province, where the outbreak began, or the surrounding area. But we are likely to find out if the virus will start spreading in these countries in the coming days and weeks.


Confirmed cases have been reported in mainland China, Hong Kong, Macau, Thailand, the US, Australia, Japan, Malaysia, Singapore, Taiwan, France, South Korea, Vietnam, Canada and Nepal. All of the recorded deaths have so far been in Hubei province.

Growing outbreak

The scale of the outbreak will depend on how quickly and easily the virus is passed between people. Using data collected up to 18 January, it appears that, on average, each person infected with the virus passes it to between 1.5 and 3.5 other people, according to an analysis by Natsuko Imai and her colleagues at Imperial College London.

Using similar estimates, Robin Thompson at the University of Oxford predicts there is a one-in-three chance that a person who brings the virus to the UK will pass it on to others in the country. That estimate is based on data collected from the beginning of the outbreak. Thompson hopes that, as countries step up measures to control the spread of the virus, the chances of this happening will become less likely.

But there is still much we don’t know about the virus, and some researchers suggest that it could spread more quickly than estimated. One study, based on data collected between 10 and 21 January, estimates that each person with the virus can pass it to between 3 and 5 other people. The work, by Shi Zhao at the Chinese University of Hong Kong and his colleagues suggests that the virus is much more contagious than originally thought.

Thompson’s estimate was calculated based on the assumption that the virus isn’t contagious until symptoms show – and this no longer seems to be the case. “If the virus is able to spread before symptoms show, that could certainly explain why the virus is spreading quicker that SARS,” says Thompson.

The US Centers for Disease Control and Prevention (CDC) cautions that, although only five cases have been reported in the US so far, person-to-person spread of the virus in the country is “likely to occur to some extent”.

Lessons from SARS

Comparisons have been drawn between the pneumonia caused by the new virus and SARS (severe acute respiratory syndrome), which infected more than 8000 people during a global outbreak that began in 2003. The viruses are from the same family, and both can cause fever and pneumonia.

So far, the new virus seems to have a lower fatality rate. Based on the number of reported cases and deaths, the rate appears to be around 2.8 per cent, compared with a 9.6 per cent rate for SARS. But it is too soon to be sure just how dangerous the virus is. We are still in the early days of the outbreak, says Thompson.

The virus is spreading more quickly than SARS. “SARS took several months to cause a thousand cases,” says Thompson. “This has caused [almost] 3000 cases in three weeks.”

The SARS outbreak was over by 2004 – there have been no reported cases since then. Health agencies brought the virus under control by isolating people with the virus, and screening air travel passengers. Such measures will be more difficult with a virus that can be spread before symptoms appear.

There is also always a chance that the virus could mutate to become more contagious or deadly. However, there is no evidence yet that the virus has mutated within people, and the World Health Organization (WHO) told a press conference last week that the virus appears to be stable.

So, how worried should we be? The WHO is still holding off from declaring a public health emergency of international concern, although the organisation says the risk of the virus is “very high in China, high at the regional level and high at the global level”.

The CDC describes the outbreak as a “very serious public health threat”. “I am pretty worried about the current situation,” says Thompson. He expects the WHO to officially declare a public health emergency if and when the virus begins to spread between people outside China. “I’m definitely nervous about it,” he says.

Slowing the spread

In the meantime, health authorities in China have undertaken unprecedented measures in an attempt to control the spread of the virus. Wuhan, where the outbreak began, has been placed on lockdown – public transport has been shut down, the airport is closed, and the use of personal motor vehicles has been banned. Immigration services in the city have been suspended in Wuhan. Several other cities have also been placed in lockdown, affecting tens of millions of residents.

Chinese authorities have also prolonged the Lunar New Year holiday. The public holiday was due to end on 30 January, but has been extended until 2 February, and schools and universities are remaining closed until further notice. A growing list of countries is screening air travellers from China. Mongolia has closed its borders with China, and the government of Malaysia has said it won’t issue visas to people from affected regions.

The Chinese government has also temporarily banned the sale of wildlife in markets and restaurants. While the origins of the virus are still unclear, it is thought that the virus was passed from bats to people, possibly via snakes or minks. All of these animals were reportedly on sale at the Huanan seafood market in Wuhan, where the first cases of the virus were reported.

The Wildlife Conservation Society (WCS) has called for the ban to be made permanent. “Poorly regulated, live animal markets mixed with illegal wildlife trade offer a unique opportunity for viruses to spillover from wildlife hosts into the human population,” Christof Walzer at the WCS said in a statement.

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Correction: This article has been amended to alter the number of countries affected.