Why ‘flattening the curve’ may be the world’s best bet to slow the coronavirus

This handout illustration image courtesy of the Centers for Disease Control and Prevention shows a transmission electron microscopic image of an isolate from the first U.S. case of COVID-19, with the spherical viral particles, colorized blue, containing cross-sections through the viral genome, seen as black dots. AFP Photo / Centers for Disease Control and Prevention

This story originally appeared on STAT, a health and medicine website that provides ambitious coverage of the coronavirus. Go here for more stories on the virus. Try STAT Plus for exclusive analysis of biotech, pharma, and the life sciences.


For many countries staring down fast-rising coronavirus case counts, the race is on to “flatten the curve.”

The United States and other countries, experts say, are likely to be hit by tsunamis of Covid-19 cases in the coming weeks without aggressive public health responses. But by taking certain steps — canceling large public gatherings, for instance, and encouraging some people to restrict their contact with others — governments have a shot at stamping out new chains of transmission, while also trying to mitigate the damage of the spread that isn’t under control.

The epidemic curve, a statistical chart used to visualize when and at what speed new cases are reported, could be flattened, rather than being allowed to rise exponentially.


“If you look at the curves of outbreaks, they go big peaks, and then come down. What we need to do is flatten that down,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters Tuesday. “That would have less people infected. That would ultimately have less deaths. You do that by trying to interfere with the natural flow of the outbreak.”

The notion that the curve of this outbreak could be flattened began to gain credence after China took the extraordinary step of locking down tens of millions of people days in advance of the Lunar New Year, to prevent the virus from spreading around the country from Wuhan, the city where the outbreak appears to have started. Many experts at the time said it would have been impossible to slow a rapidly transmitting respiratory infection by effectively shutting down enormous cities — and possibly counterproductive.

But the quarantines, unprecedented in modern times, appear to have prevented explosive outbreaks from occurring in cities outside of Hubei province, where Wuhan is located.

Since then, spread of the virus in China has slowed to a trickle; the country reported only 19 cases on Monday. And South Korea, which has had the third largest outbreak outside of China, also appears to be beating back transmission through aggressive actions. But other places, notably Italy and Iran, are struggling.


For weeks, a debate has raged about whether the virus could be “contained” — an approach the WHO has been exhorting countries to focus on — or whether it made more sense to simply try to lessen the virus’ blow, an approach known as “mitigation.”

That argument has been counterproductive, Mike Ryan, the head of the WHO’s health emergencies program, said Monday.

“I think we’ve had this unfortunate emergence of camps around the containment camp, the mitigation camp — different groups presenting and championing their view of the world. And frankly speaking, it’s not helpful,” Ryan told reporters.

Caitlin Rivers, an assistant professor of epidemiology at the Johns Hopkins Center for Health Security, said any lessening of spread will help health systems remain functional.

“Even if we are not headed to zero transmission, any cases that we can prevent and any transmission that we can avoid are going to have enormous impact,” she said. “Not only on the individuals who end up not getting sick but all of the people that they would have ended up infecting. … And so the more that we can minimize it, the better.”

On any normal day, health systems in the United States typically run close to capacity. If a hospital is overwhelmed by Covid-19 cases, patients will have a lower chance of surviving than they would if they became ill when the hospital’s patient load was more manageable. People in car crashes, people with cancer, pregnant women who have complications during delivery — all those people risk getting a lesser caliber of care when a hospital is trying to cope with the chaos of an outbreak.


“I think the whole notion of flattening the curve is to slow things down so that this doesn’t hit us like a brick wall,” said Michael Mina, associate medical director of clinical microbiology at Boston’s Brigham and Women’s Hospital. “It’s really all borne out of the risk of our health care infrastructure pulling apart at the seams if the virus spreads too quickly and too many people start showing up at the emergency room at any given time.”

Countries and regions that have been badly hit by the virus report hospitals that are utterly swamped by the influx of sick people struggling to breathe.

Alessandro Vespignani, director of the Network Science Institute at Northeastern University, is gravely worried about what he’s hearing from contacts in Italy, where people initially played down the outbreak as “a kind of flu,” he said. Hospitals in the north of the country, which the virus first took root, are filled beyond capacity, he said, and may soon face the nightmarish dilemma of having to decide who to try to save.

“This was what was really keeping me up at night, to unfortunately see Italy approaching that point,” Vespignani said, adding that now that the country has effectively followed China’s example and put its population on lockdown, “hopefully this will work.”

Vespignani, along with colleagues, published a recent modeling study in Science that showed travel restrictions — which the United States has adopted to a degree — only slow spread when combined with public health interventions and individual behavioral change. He’s not convinced that people in the United States comprehend what’s coming.


“I think people are not yet fully understanding the scale of this outbreak and how dangerous it is to downplay,” he said.

Mina agreed: “Without a very clear signal coming from our government at the national level, it’s really just like a small trickle as people start to recognize that this is happening.”

Rivers and colleagues from Harvard’s T.H. Chan School of Public Health have looked at what U.S. hospitals might endure if Wuhan-scale spread occurred in this country. Their analysis, posted on a preprint server in advance of peer review, came to a chilling conclusion.

“If a Wuhan-like outbreak were to take place in a U.S. city, even with strong social distancing and contact tracing protocols as strict as the Wuhan lockdown, hospitalization and ICU needs from COVID-19 patients alone may exceed current capacity,” they wrote. “We don’t want to go that route,” Rivers told STAT. “So it’s the top priority right now that we bend the curve.”

As of Tuesday, the Centers for Disease Control and Prevention said there had been 647 cases and 25 deaths in the country. A website maintained by Johns Hopkins University — which is considered the go-to website for Covid-19 statistics — scrapes data from a variety of sources. It suggested late Tuesday afternoon that there had been 808 cases in the U.S. and 28 deaths. Most in the deaths have been in the Seattle area.

But the reality is that with state and local laboratories in the country still getting up to speed with how to test for this infection, the full extent of spread is not known.


Without that kind of data, public officials have been loath to take the types of measures that would help to flatten the country’s epidemic curve. Those measures include banning concerts, sporting events, and other mass gatherings, closing movie theaters, telling people who can telecommute to work from home, and potentially closing schools. (The jury is still out on how much school closures would help slow spread.)

“I think that in terms of the decision-makers, we are in a place right now where we don’t have the data we wish we had in order to inform these decisions,” Rivers said. “So what I think we’re seeing is decision-makers struggling to pull the trigger on these really big, impactful decisions without having a clear sense of the current status.”

“But we know from pandemic planning and previous experiences that the sooner we implement these measures, the more effective that they are,” she said.

Mina said the lack of evidence of widespread transmission in the country may be making people feel any aggressive step right now may be an overreaction. But this is precisely the time when public health measures of this sort can have an impact, he said.

“We are all wondering if our actions are melodramatic. And we’re feeling silly,” he said, noting people still feel self-conscious bumping elbows instead of shaking hands.

“But this is the problem, that people aren’t recognizing that we are at this moment and we can make a decision right now to flatten this curve by … being OK with wondering if we’re being melodramatic,” he said.


“Should we be canceling classes? Should we be canceling our flights? Should we not be shaking hands? All of these things are things that I want the public to keep wondering if we should be doing this. Because the moment we’re no longer wondering whether we should be doing it, it’s too late,” Mina said. “That means that we know we should be doing it. And that is a bad place to be.”


Andrew Joseph contributed reporting. 

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