China coronavirus: how fast is it spreading?

24 January 2020

Interview with 

Chris Smith, University of Cambridge

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News on the emerging viral infection in China is coming in fast. The disease was first picked up by the Chinese in early December, and the source appears to be a food market in Wuhan City; the virus itself is a newly-identified member of a viral family called coronaviruses. Being a virologist himself, Chris Smith gave Phil Sansom an update on its spread...

Chris - Well what we've now learned, Phil, is a bit more about what this agent is. We know it's a member of the family of viruses known as coronaviruses. These do infect humans naturally, but they also infect lots of other animals too and they fall into three subfamilies, alpha, beta and gamma. This virus is in the beta coronavirus group of viruses. And why that matters is that there's a close relative of this virus called SARS which, some listeners will remember, was what emerged from China under extremely similar circumstances in 2002 to 2003 and spread around the world. It infected about 8,000 people. It caused about 800 deaths in more than 50 countries. This new virus is about 90% similar to SARS when we've read the genetic code for it. And because of the connection to this food market, we know that there was a probably under the counter trade going on in illegal and other wildlife species in that market. So what scientists are suggesting is that probably a consignment of animals, most likely bats, were brought to that market, those bats have infected either humans directly, or an intermediate animal, and that intermediate animal has become very infectious and then pass the infection onto people. And what we're now seeing is onward transmission because we've got evidence that this virus is spreading from people who caught it into other people who've had contact with those people.

Phil - Those were some pretty scary figures obviously that you just mentioned for SARS, 800 deaths out of 8,000 cases. Is this new virus, from what we can tell so far, as dangerous and will it spread as widely do you think?

Chris - Overall, the number of people dying is not as high as it was for SARS, which was about 10%. It seems to be about 5%. Also, the people who are succumbing to this, many of them are vulnerable already. They are elderly or they have other health problems. But it is early days and that could change because the other thing about these viruses is they can mutate. They're finding a home now in a new host, and that is us. And there's every reason to be suspicious that as they learn to live in their new home, they're going to change genetically. And that will rewrite the rules of the ballgame.

Phil - And do you know how many people roughly have been infected so far?

Chris - We're very reliant on data from China. Now you take that with a pinch of salt because we know that when SARS happened in China, China knew about that for many months before they told the rest of the world. And that's probably part of the reason why SARS managed to gain such a toehold and spread so far before it was clamped down on. They have been more open and they have been more transparent with this outbreak. But at the same time, you always have to be cautious about just swallowing the figures that are passed to us. We know now they're talking about thousands of cases that they have confirmed in China, but when one looks at the news of what's happening in China, you see lockdown of entire areas of the country and them saying, "We're now going to build a new hospital with a thousand beds in it and we're going to do it in two weeks." Now that's a major undertaking and that suggests that they're very concerned.

Phil - Obviously some of the people listening to our show will fit into those categories that you mentioned earlier, people more at risk, maybe people who are older. How worried should they be even if they live nowhere near China?

Chris - Well, I think one should never be complacent with an emerging infection because this is something which has never circulated in the human race before. No one is immune to this and it is a moving target. It could mutate, it could change and so one has to be very cautious about saying it's going to be terrible, but one shouldn't be complacent and say it's probably going to be fine. What we can say is a) we know about it, b) we know that we can make vaccines against agents like this, because there's an experimental vaccine that appears to work against the Middle Eastern coronavirus, so I think given that we're watching for it and we are quite well prepared I would say, I would reassure people, but at the same time don't take it for granted.

Phil - We've also had a question in from a listener for you, Chris. Jim Hungerford sent us this.

Jim - Hi Chris. I was wondering about R0 for the new coronavirus. How can that be measured as a single number, When I would have thought it'd vary dramatically depending on the particular situation, like if people are crowded together or if they're particularly susceptible because of the weather? Many thanks.

Phil - What's he talking about there? What's an R0?

Chris - R0 stands for the reproduction number. In other words, when a person is in the community and they're infected with something, how many new cases of that infection will they cause as a direct consequence of having the infection? If the R0 number is greater than one, that means the outbreak is going to increase because for every case there's going to be more cases than you started with. On the other hand, if the R0 number is less than one, the infection is going to dwindle and it will just fizzle out.

Phil - So if every infected person infects two other people then R0 equals two?

Chris - Correct.

Phil - So do you know anything about what it is for this Wuhan coronavirus?

Chris - We don't. And the reason we don't know is because it's early days. The data are patchy and they're going to be based on certain geographies in China. And the point that Jim is making in his question is, surely there's going to be different parts of the world with different populations and the virus will behave differently. Or when we talk about making these R0 values, we're talking about an average. So we would see how this thing performs, and as we gain more understanding, we would compute a more accurate R0 value. For measles for example, you're into double figures. That's one of the most infectious viruses we know. SARS, it was down at single figures, maybe between 1 and 5. It was very low. Flu is about 5 on a bad year. And so therefore, we're looking at a number which is probably going to be down in those low numbers I would say, based on the trajectory this thing appears to be taking. But it is early days and that's just my speculation.

Phil - Finally, have you got a quick take home message for someone who has seen a lot of news about this virus and isn't quite sure what to make of it?

Chris - First of all I wouldn't panic, and secondly, I also wouldn't waste your money on a face mask, unless you're going to go and buy one of these proper fit tested PPE masks, which forms a proper seal around your nose and mouth and you're going to wear eye protection. And the reason eye protection matters is because your tear ducts drain into your nose. So any viruses that land on your eyes, if they can't infect your eyes, they can still drain into your nose and infect you via that route. So don't waste money on one of these dopey face masks. Go and buy a pint of lager and sit in the pub. It'll cost you probably less. It'll protect you from the virus equivalently well, and you'll also enjoy it more.

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