The US and others continue to tighten travel restrictions to China and have increased warnings over the coronavirus outbreak that first emerged in China in December.

The World Health Organization reported that there are now more than 7,700 confirmed and more than 12,000 suspected cases of the flulike coronavirus (known as 2019-nCoV or 2019-nCoV acute respiratory disease) throughout China.

Related: What to call this new coronavirus? Some cautionary tales.  

And on Thursday, WHO declared the outbreak a global emergency. The death toll has risen to 170 — all in China. The country is by far bearing the biggest burden with only about 100 cases having been reported outside the country.

Related: The global ripple effects of the coronavirus outbreak

The ripple effects of the outbreak are being felt all over the world, from tourism to entertainment to supply chains — with major companies like South Korea's Hyundai Motors announcing plans to halt some production to cope with the disruption. And in the US, government authorities announced that they are quarantining about 195 passengers returning to the country from Hubei province.

Related: When will there be a coronavirus vaccine? 5 questions answered.

So, let's get a reality check. Just how serious is this virus really, and what's the best way to prevent its spread? Michael Mina, a physician at Brigham and Women's Hospital in Boston and an infectious disease specialist who studies viruses like this one, spoke to The World's Carol Hills and discusses what's known at this point about this disease, and the best ways to respond.

Carol Hills:  The World Health Organization declared the coronavirus a worldwide public health emergency. But the director of the WHO also said the organization opposes any restrictions for travel or trade or other measures against China. So, as an infectious disease specialist, how can those two things be true? It's an international public health concern, but they think people should not restrict travel or trade.

Michael Mina: So there's a couple of reasons for that. On the one hand, it makes sense to say that we should be restricting travel and trade if there's a big outbreak going on in China. But, one of the major points here is that this pathogen is potentially spreading so well that there's concern that even if we were to restrict all travel in and out of China, sort of the cat's already out of the bag, if you will. And it's likely that these very severe travel restrictions might not actually do as much as we might hope to prevent further spread.

But is it also trying to say 'don't panic, everybody. This virus is controllable, so continue trade and travel'? Or is it trying to make a kind of scientific comment by saying it's not really worth restricting trade and travel?

I think the decision to use that sort of language is the WHO, and all public health agencies have to really walk a very fine line between being realistic about how much this pathogen may spread versus what's the real impact of this pathogen. And even with all we know today, we still don't actually know — is this really very bad for people or are we just seeing a really small slice of severe infections? And is this going to become more like seasonal infection? And so, I think there's a real balance that needs to be had in terms of what sort of level we want to really think about, just how severe we need to place restrictions. And we don't want to, for example, restrict people's movements so much that we start getting into the territory of human rights violations and things like that.

I think a lot of people are trying to understand how serious is this new virus. I mean, a lot of people who live thousands and thousands of miles away from China.

Frankly, scientists, including myself, and more or less all scientists who are studying this at the moment, are also trying to understand how severe is this. What we know is that currently there's been around 10,000 reported cases, for example. And, around 200 of those cases have led to deaths. Now, that sounds very, very scary. But what is not — as a parent, and it's very difficult to measure — is just how many real cases are there truly? It's possible, for example, that there may be 100,000 or more cases going on currently or that have already happened. And although that sounds scary, what that means is that if there's actually been 100,000 cases, that means the vast majority of them have been totally asymptomatic, kind of like a normal flu season. You might have very mild symptoms in some people and then a very few will actually go to the hospital.

Let's get down to the reality check. How is the coronavirus spread? What do we know about that?

So, the coronavirus is a respiratory virus and it's spread in droplets. So, when somebody coughs who has it, those droplets will fly out of somebody and potentially be inhaled or otherwise contact somebody else. It can also be spread on surfaces. If somebody coughs on a doorknob, or wipes their nose and then opens the door, somebody behind them might touch it and wipe their own nose, for example, or touch their face. Which is why, taking precautions is so important during an outbreak like this. We want to make sure that everyone's washing their hands as much as possible and trying not to touch their face as much as possible.

And what are the symptoms of the coronavirus?

So, the symptoms are generally a bit like a flu virus. People get a cough, they get fever, and generally an achy feeling. If you get a severe infection, though, then some of the symptoms become much more apparent. Things like respiratory distress — you start having trouble breathing. But that's sort of going in a more severe direction.

And compared to other viruses that you've studied or know about, how deadly is the coronavirus?

Yeah, so coronavirus is a family of viruses. So, coronaviruses are one of the viruses that normally spread in children and don't cause any deaths. This particular virus, we still don't know. And that's where we really need to understand the full denominator. So far, we've seen amongst hospitalized or medically attended patients who actually go and get a diagnosis, the death rate has been around 2%, which is high, but it's actually not too much higher than the flu virus in terms of people who present to the hospital and become admitted into the hospital with flu. The mortality rate amongst those people is actually 7%. So, the mortality due to this virus is potentially in the realm of flu. Once we have a better understanding of the true numbers of cases that are occurring out in the population who aren't necessarily symptomatic, we'll have a better understanding

What's the mortality rate among other viruses that people would know about?

So, different viruses have very different mortality rates. For example, Ebola, which we've all heard about because of recent epidemics and outbreaks, is somewhere around 30% or so. SARS, at least according to the case counts that we had, was also very high. Depending on the data that's being used, it could have been upwards of 30% of hospitalized patients or more. Measles, for example, was actually very high, dependent on data for where in the world and what the underlying conditions of the children are who got it. In 2019, the average death rate of measles was actually 1 in 100. It's very high.

Now, who is most prone to get seriously sick from the coronavirus?

Yeah, that's a terrific question. So, the coronavirus, this current one, as well as SARS and MERS, which were two previous outbreaks that happened due to novel coronaviruses, they all seem to have this peculiar pattern of infecting older individuals — which is really distinct. Normally, we think of many viruses as being childhood infections that really harm children. But the pattern here is peculiar. We're not exactly sure why, but it does seem to be mostly older individuals and those with comorbidities, meaning previously existing conditions.

Now, you've said you don't know how deadly it is — particularly, because you just don't have the true numbers of who's been infected — so, how do you manage a situation like this? You don't know the key things about a disease in moments like this — you know, the really important things. So, it seems like it is human nature to kind of panic. What do we do about this really tough situation?

Yes. So humans are certainly most afraid of the unknown, I would say. And, in this case, I think the best thing that we can do to best deal with this pathogen and this virus that's transmitting is to a certain extent take it one day at a time. We can project out our estimates of where this pathogen might be going or how many people that might be infecting. But at the end of the day, a lot of it is based on unknowns. And so, what we're trying to do is have as concrete information as we can in any given day and give the right information to the public on a day-by-day basis. And I think that underlies a bit of what appears to be conflicting language that comes from public health policymakers and other bodies like the WHO. Where, it seems on the one hand, they're saying this is very serious — it's a global health emergency. And at the other side of the spectrum, they're saying, however, maybe don't restrict travel so much to China, it might not be beneficial. And I think that's always the tension in public health. There's this balance between giving as much information as we can to the public at the time we know that information without projecting too much into the future because it could go in different angles.

What advice do you have for people right now outside of China in terms of how one should or shouldn't be preparing?

I think one of the best ways to prepare is to just keep abreast of all of the knowledge and the information that's coming out. Make sure you're reading multiple different media sites and don't get trapped into reading information that might be misinformation. There's been a lot of fearmongering in this outbreak mostly because of social media and the spread, the rapid dissemination of both good and false information. 

So, I think one of the important things is to find reliable resources like the CDC website, WHO, Johns Hopkins, Harvard; each have good information on their websites about this virus, So that’s one thing. The other thing is, I do agree not to panic.

Outside of China, there’s been extraordinarily small numbers of cases relative to the human population that have been diagnosed. And so, we just don't know, is this actually going to spread in the United States? That's still an unknown. And so at the moment, there's really no need to panic because there's nothing to do anyway. We just have to take a step back and wait to see. Does this actually start to spread? And then we'll give the information as quick as we know it to the public.

This interview has been edited and condensed for clarity. 

Update: This interview has been updated with a video recording of a Facebook live with Michael Mina and The World's Elana Gordon the Harvard's T.H. Chan School of Public Health.

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