There’s one country in the world that currently has the most knowledge of and experience with Covid-19: China.

China, and specifically Hubei province, is where the Covid-19 disease emerged; it’s where 83 percent of the 89,000 cases known to date have been recorded; and it’s where doctors and health authorities have been battling an epidemic for two months — while other countries braced themselves for outbreaks — using unprecedented public health measures, including a cordon sanitaire and lockdowns that affected millions.

In recent weeks, though, the number of new infections and deaths reported in China has been declining, which suggests spread of the virus may have peaked there and that transmission is slowing down.

At the same time, cases are rapidly increasing in several other countries, with major outbreaks in South Korea, Italy, and Iran — and a growing case count in the United States.

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It’s now critical that the rest of the world learn as much as it can from China’s efforts to respond to and limit the spread of the virus.

That was precisely the intention of a recent World Health Organization (WHO) mission to China, led by the agency’s assistant director general and veteran epidemiologist Bruce Aylward. Its major finding: “China’s bold approach to contain the rapid spread of this new respiratory pathogen has changed the course of a rapidly escalating and deadly epidemic.”

On Monday, Vox talked to Aylward about the big takeaways from the mission’s report: the playbook China used to curb Covid-19 spread, why speed in responding to an outbreak is so crucial, whether we can trust China’s data, and why smoking could be exacerbating the impact of the epidemic there. Our conversation has been edited for length and clarity.

What the world can learn from China’s Covid-19 response

Julia Belluz

The WHO has been suggesting the world should follow China’s lead, but as you know, there are concerns about the human rights effects from China’s response to the Covid-19 outbreak — most notably, the restrictions on freedom of movement through lockdowns and cordon sanitaires. How do you respond to critics who are concerned about that?

Bruce Aylward

I think people aren’t paying close enough attention. The majority of the response in China, in 30 provinces, was about case finding, contact tracing, and suspension of public gatherings — all common measures used anywhere in the world to manage [the spread of] diseases.

The lockdowns people are referring to — the human rights concerns — usually reflect the situation in places like Wuhan [the city in Hubei province where the virus was first detected]. [The lockdown] was concentrated in Wuhan and two or three other cities that also exploded [with Covid-19 cases]. These are places that got out of control in the beginning [of the outbreak], and China made this decision to protect China and the rest of the world.

China is now trying to restart its economy. They can’t do that with millions of people in lockdown in their apartments or with the trains stopped and all their factories suspended. They are getting those things working again, but they have their system primed for rapid detection and rapid response. They never want to be in another situation like a Wuhan — and they haven’t. That’s the first place, and 30 other provinces managed to avoid that, and not just avoid that but reverse the [outbreak].

Julia Belluz

Okay, so most of the measures used in China to stop the virus were traditional public health moves that are broadly accepted — and the draconian measures were rarer. Is there any sense of what in China’s toolkit was most effective?

Bruce Aylward

I think the key learning from China is speed — it’s all about the speed. The faster you can find the cases, isolate the cases, and track their close contacts, the more successful you’re going to be. Another big takeaway is that even when you have substantial transmission with a lot of clusters — because people are looking at the situation in some countries now and going, “Oh, gosh, what can be done?” — what China demonstrates is if you settle down, roll up your sleeves, and begin that systematic work of case finding and contact tracing, you definitely can change the shape of the outbreak, take the heat out of it, and prevent a lot of people from getting sick and a lot of the most vulnerable from dying.

The question becomes, then, how did they do that, and how much of it is replicable? Since coming back from China, everybody I talk to begins with, “We can’t lock down a city of 15 million people like China.” I say, “Why would you ever want to?” And I ask, “Does your population know x, y, z [about the virus]?” I learn they haven’t started with the basics.

So, No. 1, if you want to get speed of response, your population has to know this disease. You find any population in the West and ask them what are the two presenting signs you have to be alert to. What would you say?

Julia Belluz

Aren’t the two initial symptoms most commonly fever and dry cough?

Bruce Aylward

Right. [But many still think] it’s a runny nose and cold. Your population is your surveillance system. Everybody has got a smartphone, everybody can get a thermometer. That is your surveillance system. Don’t rely on this hitting your health system, because then it’s going to infect it. You’ve got this great surveillance system out there — make sure the surveillance system is primed. Make sure you’re ready to act on the signals that come in from that surveillance system. You’ve got to be set up to rapidly assess whether or not they really have those symptoms, test those people, and, if necessary, isolate and trace their contacts.

Here, again, is where I’ve seen things starting to break down. What I’ve been told is if you think you’ve been exposed and have a fever, call your [general practitioner]. We’ve got to be better than that. If we are going to use our GPs — do they have an emergency line where you can get through? Do they know what to do?

In China, they have set up a giant network of fever hospitals. In some areas, a team can go to you and swab you and have an answer for you in four to seven hours. But you’ve got to be set up — speed is everything.

So make sure your people know [about the virus]. Make sure you have mechanisms for working with them very quickly through your health system. Then enough public health infrastructure to investigate cases, identify the close contacts, and then make sure they remain under surveillance. That’s 90 percent of the Chinese response.

Julia Belluz

But, again, China implemented so many different measures at once. How do we know contact tracing was more important than, say, the mass cordon sanitaire and shutting down cities?

Bruce Aylward

Think about the virus. Where is the virus, and how do you contain the virus? You know the virus is in the cases and in the close contacts. That’s where the majority of the virus is; that’s where the majority of the focus should be. China did a whole bunch of things, and other countries may have to do them, too, as they go forward. But the key is public information and having an informed population, finding those cases, rapidly isolating them. The faster you isolate them is what breaks the chains. Making sure close contacts are quarantined and monitored until you know if they’re infected. Somewhere between 5 and 15 percent of those contacts are infected. And again, it’s the close contacts, not everyone.

Julia Belluz

There were reports from China about collateral damage from this outbreak — the HIV patients, for example, who were reportedly not getting treatment in time because of travel restrictions and lockdowns. What can we learn from China to minimize this type of damage in other countries?

Bruce Aylward

China took a whole bunch of steps when they realized they had to repurpose big chunks of their hospital systems to [respond to the outbreak]. The first thing is, they said testing is free, treatment is free. Right now, there are huge barriers [to testing and treatment] in the West. You can get tested, but then you might be negative and have to foot the bill. In China, they realized those were barriers to people seeking care, so, as a state, they took over the payments for people whose insurance plans didn’t cover them. They tried to mitigate those barriers.

The other thing they did: Normally a prescription in China can’t last for more than a month. But they increased it to three months to make sure people didn’t run out [when they had to close a lot of their hospitals]. Another thing: Prescriptions could be done online and through WeChat [instead of requiring a doctor appointment]. And they set up a delivery system for medications for affected populations.

Is this the big pandemic we’ve been told is coming — the “big one”?

Julia Belluz

The idea that the spread of this virus is driven mainly by families features prominently in your report. How do we know that?

Bruce Aylward

You look at the big, long lists of all the cases and identify those where you have clusterings in space and time and try to investigate what kind of clustering happened: Was it in a hospital, an old-age home, theaters, restaurants? We found it was predominantly in families. It’s not a big surprise; China had shut down a lot of the other ways people could gather. And family clusters are the closest, longest exposures [to the virus], and getting the virus is a function of whether someone’s got it, how long they’re exposed, and how much virus they are shedding.

“This is a disease that is in the cases and their close contacts. It’s not a hidden enemy lurking behind bushes.”

More of a surprise, and this is something we still don’t understand, is how little virus there was in the much broader community. Everywhere we went, we tried to find and understand how many tests had been done, how many people were tested, and who were they.

In Guangdong province, for example, there were 320,000 tests done in people coming to fever clinics, outpatient clinics. And at the peak of the outbreak, 0.47 percent of those tests were positive. People keep saying [the cases are the] tip of the iceberg. But we couldn’t find that. We found there’s a lot of people who are cases, a lot of close contacts — but not a lot of asymptomatic circulation of this virus in the bigger population. And that’s different from flu. In flu, you’ll find this virus right through the child population, right through blood samples of 20 to 40 percent of the population.

Julia Belluz

If you didn’t find the “iceberg” of mild cases in China, what does it say about how deadly the virus is — the case fatality rate?

Bruce Aylward

It says you’re probably not way off. The average case fatality rate is 3.8 percent in China, but a lot of that is driven by the early epidemic in Wuhan where numbers were higher. If you look outside of Hubei province [where Wuhan is], the case fatality rate is just under 1 percent now. I would not quote that as the number. That’s the mortality in China — and they find cases fast, get them isolated, in treatment, and supported early. Second thing they do is ventilate dozens in the average hospital; they use extracorporeal membrane oxygenation [removing blood from a person’s body and oxygenating their red blood cells] when ventilation doesn’t work. This is sophisticated health care. They have a survival rate for this disease I would not extrapolate to the rest of the world. What you’ve seen in Italy and Iran is that a lot of people are dying.

This suggests the Chinese are really good at keeping people alive with this disease, and just because it’s 1 percent in the general population outside of Wuhan doesn’t mean it [will be the same in other countries].

Julia Belluz

That’s really concerning for the rest of the world. Are you suggesting this is the big one — the once-a-century pandemic people have been bracing for?

Bruce Aylward

It’s not. It can be the big one but like, for flu — whether you have a pandemic with flu, it’s a function of the virus. That’s a virus with a very, very high infectivity rate, a very, very high transmissibility rate. The time [the virus] takes to go from [one person to the next] can be as short as 1.5 days. For Covid-19, it’s longer — four to five days. Look around the world. We’re seeing a whole bunch of outbreaks controlled with the right responses, and even turned around if they get to a bad state.

Panic and hysteria are not appropriate. This is a disease that is in the cases and their close contacts. It’s not a hidden enemy lurking behind bushes. Get organized, get educated, and get working.

Julia Belluz

How should countries look out for the virus?

Bruce Aylward

Originally, I was a big believer in the idea that we should swab millions and see what’s going on [how many have the virus]. But the data from China made me rethink that. What could be done instead is that every hospital should test people with atypical pneumonia for Covid. People with flu-like symptoms — test for Covid.

We have a lot of surveillance systems for flu in the world, trying to pick up the big one, and should use those systems to test for Covid.

Trusting China

Julia Belluz

We have been seeing a small uptick in Hubei for the last couple of days. What is going on there?

Bruce Aylward

I wrote to the [team] in China yesterday and asked them about the uptick in cases, which was very slight. They said they are getting through the backlog of suspect cases — so people who had clinical symptoms, CT scan findings — and rather than clinically confirming them, they are making sure they test them. Some of them are also in some of those prison outbreaks. But the big driver is coming off the suspect cases. In 48 hours, [we’ll know if that] theory is true. Already today, cases started to come down. The [new case count] dropped again today.

Julia Belluz

Can we trust China’s data?

Bruce Aylward

The big question is, are they hiding things? No, they are not. We looked at many different things to try to corroborate that cases are dropping. When I went to fever clinics and talked to people working there, they’d say, “We used to have a line out the door, and now we see a case once per hour.”

According to the national data, fever clinics went from seeing 46,000 people per day at one point and it’s now down to 1,000. So there’s been a huge drop in numbers into the feeder system.

Second thing: When talking to physicians in hospitals, I heard again and again that we have open beds, we can get people isolated even more rapidly. I heard that in Wuhan and other provinces. The third thing: I talked to people running clinical trials of drugs, and they are having a problem recruiting patients. All these things helped corroborate [China’s data].

Julia Belluz

What were the biggest vulnerabilities in China, and what are you most worried about for other countries as they face more cases?

Bruce Aylward

You have to have enough beds. In China, they closed off whole wings [of hospitals], sealed them to make them a dirty zone [where patients with the disease could be treated safely]. They worked at scale. They bought a heap of ventilators to keep people alive. They made sure they had a lot of high-flow oxygen, CT-scanning capacity, lab capacity. So beds, ventilators, oxygen, CTs, and labs. And they had problems with all of those supplies at different points. [The Chinese] will say there are shortcomings in our response, in how fast we found this, how fast we responded. And there will be a major reform to address that.

Why the virus disproportionately kills the elderly and spares the young

Julia Belluz

While deaths are occurring at higher rates in elderly people, there have been reports of young, otherwise healthy people dying, too. What’s going on there? And is there any talk of how China’s high smoking rates may be contributing to these deaths?

Bruce Aylward

[Smoking] definitely does because the co-morbid conditions makes [Covid-19] worse. Over the long term, we know smokers get cardiovascular and lung disease, and these are all co-factors in terms of a higher probability of mortality. From that perspective, we know it’s a problem. In some of the mortality [research,] we see a higher mortality rate in males than females in China. There’s a suspicion that may be a function of differences in smoking patterns: There’s very high smoking rates among men in China compared to women.

We spent a lot of time asking doctors who these people in their 30s and 40s are who are rapidly progressing and getting this disease and dying. They’d say, “We don’t know.” I’d ask, “What about smoking?” I never found one who said yes to that question. It’s something I couldn’t get an answer to.

Julia Belluz

What are the other important knowledge gaps?

Bruce Aylward

It’s hard to find the virus in general swabs done in the community. And that’s interesting and reassuring. It’s not like flu. But we couldn’t answer the question of why some young, otherwise healthy people suddenly deteriorate. We need to understand that if we [want to] keep people alive.

Julia Belluz

In the elderly, what explains the high death rate? Is it something about deterioration of the immune system with age or the higher probability you have [of developing] other illnesses as you age?

Bruce Aylward

I think it’s the latter. These people are dying of an inflammatory process in their lungs. It’s not an infectious process, like a bacterial or viral infection. It’s inflammatory, like we see with SARS. We’re not sure of the mechanism. We do know the proportion of people who die who had cancer was half compared to hypertension and cardiovascular disease. Diabetes is a little bit lower than those two, and cancer lower again.

Julia Belluz

So why do kids seem to be spared so far? What’s the best hypothesis?

Bruce Aylward

It’s a million-dollar question. There are three possibilities: Kids don’t get infected for some reason; they get infected but have a low expression of disease; they get infected and express disease like everyone else but we haven’t seen it because of schools being closed. I think the first and last aren’t the reality. So it’s that middle group.

There are a couple of theories going around [to explain this]. The receptors [Covid-19] binds to in the lungs aren’t very mature in children. But the reality is we see this phenomenon up to 90 years of age, so that sounds unlikely. Second, maybe the four coronaviruses that cause colds confer some temporary immunity in kids. But then why aren’t the elderly [protected]?

We’ve got to get an antibody test [to test the population for antibodies to the virus] to know if kids are driving the epidemic and we just can’t see it.

Correction 3/2: A graphic in this piece previously misstated the percentage of cases in China that were not linked back to the Wuhan area. The graphic has been updated with the correct figure, 14 percent.