clock menu more-arrow no yes mobile

Filed under:

Flattening the curve isn’t good enough

The case for an actual coronavirus suppression strategy.

Baseball games without spectators are taking place in Taiwan, amid the coronavirus pandemic.
Sam Yeh/AFP via Getty Images

Americans adopted a mantra early in the coronavirus pandemic that we need to “flatten the curve” — shorthand for agreeing to social distance as much as possible to save lives.

The goal is to slow the spread of the virus so hospitals and doctors don’t become overwhelmed with a surge in patients. The strategy saves lives through mitigation, reducing the harm the virus causes. It also makes it possible for patients to receive the best treatment available because there are fewer of them in the hospital at any one time.

The approach, though, still assumes that many people will still get sick and suffer — and that many people will die.

Mitigation is important, but it is not suppression — a strategy designed to beat the virus into submission. The United States has not had a serious public debate about this distinction. It needs to.

The goal of suppression is to lower the number of new cases, not just draw out the time it takes for them to appear. Social distancing is one piece of a suppression strategy. But it’s not enough. Suppression requires not just social distancing but contact tracing and case isolation to keep pushing numbers lower and lower — eventually allowing society to return to a quasi-normal life, confident that it can quash new outbreaks.

The US is debating how and when to reopen the economy. But first, it needs to figure out a public health response of suppression first. It’s time to move beyond “flatten the curve” to a new mantra: “Suppress the virus.”

Mitigation: Stop the hospital system from becoming overwhelmed

In early March, when Seattle and the Bay Area had adopted strict social distancing policies but most of the country hadn’t, many public health officials were talking enthusiastically about mitigation.

The goal, in their own words, was not so much to reduce the total share of the US population that got infected but to slow the pace at which infections occurred.

Here’s how Dylan Scott and Eliza Barclay reported it for Vox on March 10:

The main uncertainty in the coronavirus outbreak in the United States now is how big it will get, and how fast. The Centers for Disease Control and Prevention’s Nancy Messonnier told reporters on March 9, “many people in the US will at some point, either this year or next, get exposed to this virus.”

According to infectious disease epidemiologist Marc Lipsitch at Harvard, it’s “plausible” that 20 to 60 percent of adults will be infected with Covid-19 disease. So far, 80 percent of cases globally have been mild, but if the case fatality rate is around 1 percent (which several experts say it may be), a scenario is possible of tens or hundreds of thousands of deaths in the US alone.

Yet the speed at which the outbreak plays out matters hugely for its consequences. What epidemiologists fear most is the health care system becoming overwhelmed by a sudden explosion of illness that requires more people to be hospitalized than it can handle. In that scenario, more people will die because there won’t be enough hospital beds or ventilators to keep them alive.

A disastrous inundation of hospitals can likely be averted with protective measures we’re now seeing more of — closing schools, canceling mass gatherings, working from home, self-quarantine, self-isolation, avoiding crowds — to keep the virus from spreading fast.

This was illustrated with widely popular “flatten the curve” charts, depicting a massive campaign to prevent hospital resources from becoming overtaxed by a sudden surge in cases.

Many media outlets developed versions of this chart, all adapted from earlier work by the CDC with reference to flu pandemics.

As Carl Bergstrom, a biologist at the University of Washington, tweeted, the power of this graphic is that it demonstrates how measures to reduce the spread of the virus can save many lives “even if you don’t reduce total cases.”

Deaths, after all, are a function of both the volume of cases and the case fatality rate. If the number of cases rises so high that the case fatality rate starts to spike — if a city runs out of ICU beds or ventilators or appropriately trained nurses — then many more people will die than if the curve gets flatter.

Mitigation also might reduce the number of total cases. People are hopeful that a Covid-19 vaccine will be available sometime in 2021. If that happens, the right arm of the curve would essentially be truncated and reduce the total number of people who get sick.

But the power of curve-flattening as a concept is that it doesn’t rely on that. It shows that many lives can be saved even if 60 to 70 percent of the population gets sick before herd immunity halts further spread of the virus.

A natural complement to flattening the curve is trying to “raise the line” by increasing the health care system’s capacity to treat Covid-19 cases.

Raising the line is a multifaceted task — canceling or delaying elective procedures, training additional medical personnel, constructing improvised hospitals, boosting production of personal protective equipment, and manufacturing additional ventilators and moving them smartly around the country to where they’re needed.

You can think of it as working in two different ways. One is that even a flattened curve might still peak above health system capacity (this appears to have happened in Wuhan, China; Lombardy, Italy; and to an extent in New York City), in which case efforts to raise the line directly save lives.

The other is that the height of the line determines how much flattening needs to be achieved to save lives. A higher line means that not much flattening is needed, so social distancing measures can be less extreme without risking overwhelming the health system.

Mitigation still means a lot of deaths

If the sole goal of American policy is to prevent hospitals from becoming overwhelmed, then in most of the country, things may be on track. Even as the United States has become the country with the highest number of confirmed Covid-19 cases, the rate of growth — as depicted by the bending of the line on a log scale chart — has clearly declined.

Rani Molla and Dylan Scott/Vox

A few states — mostly in the urban Northeast — are using close to all of their ICU beds and need case volumes to fall further to maintain health system capacity. But much of the country, including major blue states like California and major red states like Texas, are well below the level at which they would run out of hospital capacity and send deaths skyrocketing.

California, for example, has been exporting ventilators to other states with greater needs. And even in New York, where hospital capacity was under pressure, emergency line-raising measures like ad hoc field hospitals and the dispatch of the USNS Comfort to the city turned out to be mostly unnecessary.

One reason for this is that in practice, the hospitalization rate for Covid-19 cases seems to be lower than modelers estimated five or six weeks ago, even though the fatality rate is roughly in line with expectations.

Unfortunately, what we’ve seen is that even when hospital systems aren’t overwhelmed and people are able to receive good care for Covid-19, many people still die. And if more people get sick, then more people will die.

At the current levels of infection, the United States does not have major hospital capacity problems. And it’s plausible that measured reopening steps underway in many states are, if prudently implemented, compatible with the country more or less plateauing at the current rate of infection and avoiding the hospital breakdown nightmare scenario.

But more than 1,500 Americans are dying every day from Covid-19, and research into “excess deaths” makes it pretty clear that the true figure is likely over 2,000. Project that out to a year and the US death toll will land at around 800,000.

As Bergstrom and Natalie Dean, a biostatistician at the University of Florida, explained in a recent New York Times op-ed, allowing enough people to become infected to achieve herd immunity would likely result in a significant number of carryover infections and well over a million deaths.

A vaccine or a super-effective treatment drug might come along before that happens. But the widely cited 18-month vaccine timetable is already very optimistic. Barring some kind of unforeseen breakthrough, even a successful mitigation strategy could involve a death toll that’s dramatically higher than what anyone active in politics is contemplating. The alternative strategy is to not just flatten the curve but drive the number of cases down to zero.

Some countries are stomping on the curve

Hong Kong, by contrast, over the past three weeks has seen zero new cases on most days.

Under the circumstances, the island is steadily moving to reduce restrictions. As of May 1, a rule requiring restaurants to remain half-empty has been lifted, and now a slightly laxer policy is in place, allowing dine-in service as long as tables remain 1.5 meters apart. And not only are restaurants opening, people are clamoring to get out and eat.

With the disease seemingly beaten back domestically, Hong Kong is now in a position to start switching emphasis to a strategy focused on border controls. With the pandemic still raging globally, the city can’t let its guard down entirely. And because Hong Kong is so small and dependent on international commerce, just opening up the domestic service economy can’t really save the city from serious economic problems.

But the city has a clearly articulated strategy that it calls “suppress and lift”: ease restrictions now when cases are at zero, but then clamp back down as necessary to push cases back down if they pop up.

Taiwan has also had no new cases for several days, and since April 6, all of Taiwan’s reported cases have stemmed from a single naval vessel’s goodwill mission to the island of Palau rather than community spread. New Zealand has not done quite this well, but the government believes it has successfully identified and isolated all of the country’s coronavirus cases and is lifting restrictions, on the claim that the virus has been “eliminated” in the country.

South Korea’s outbreak is now down to single-digit numbers of new cases per week, and a key test for the country is whether an anticipated surge of holiday travel this week to the island of Jeju (a major Korean tourist destination) will lead to a new wave, or if the peninsula can suppress spread of the disease. South Korean professional baseball also resumed this week, though without fans in the stands.

The United States, meanwhile, is moving to open up on the basis of a vaguely articulated assumption that settling for mitigation is good enough.

One reason for the pressure to open up is that while widespread orders to shelter in place have clearly succeeded in slowing the spread of infection, they’re not bringing case volumes down quickly. Authorities fear the economic pain of prolonged shutdowns, and it seems like the mass public is growing impatient and starting to bend the rules.

But the reality is that the United States has not really tried the strategies that have made suppression successful. To accomplish that, America would need to invest in expanding the volume of tests, invest in more contact tracers, and create centralized quarantine facilities so that infected people aren’t simply sent home to infect the rest of their household.

Since the US didn't spend April doing that, trying to achieve suppression — along the lines of Taiwan, Hong Kong, Korea, and New Zealand — would necessarily involve more delay and more economic pain. But doing so would save potentially tens or hundreds of thousands of lives and almost certainly lead to a better economic outcome by allowing activity to truly restart.