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Coronavirus: What is 'flattening the curve,' and will it work?

Flattening the curve refers to community isolation measures that keep the daily number of disease cases at a manageable level for medical providers.
Flattening the curve refers to community isolation measures that keep the daily number of disease cases at a manageable level for medical providers.
(Image: © CDC)

Efforts to completely contain the new coronavirus — the pandemic responsible for infecting hundreds of thousands of people in 130 countries with the disease, called COVID-19 — have failed. 

In less than a month, the global number of confirmed COVID-19 cases doubled from about 75,000 cases on Feb. 20 to more than 153,000 on March 15. That infection rate, scary as it sounds, hides just how much the out-of control virus has spread, especially in the hardest-hit communities. In Italy, for example — the country with the worst COVID-19 outbreak outside of China — confirmed cases doubled from 10,000 to 20,000 in just four days (March 11 to March 15). 

This rapid growth rate in Italy has already filled some hospitals there to capacity, forcing emergency rooms to close their doors to new patients, hire hundreds of new doctors and request emergency supplies of basic medical equipment, like respirator masks, from abroad. This lack of resources contributes, in part, to the outsize COVID-19 death rate in Italy, which is roughly 7% — double the global average, PBS reported.

Related: Live updates on COVID-19

Health officials take for granted that COVID-19 will continue to infect millions of people around the world over the coming weeks and months. However, as the outbreak in Italy shows, the rate at which a population becomes infected makes all the difference in whether there are enough hospital beds (and doctors, and resources) to treat the sick. 

In epidemiology, the idea of slowing a virus' spread so that fewer people need to seek treatment at any given time is known as "flattening the curve." It explains why so many countries are implementing "social distancing" guidelines — including a "shelter in place" order that affects 6.7 million people in Northern California, even though COVID-19 outbreaks there might not yet seem severe.

Here's what you need to know about the curve, and why we want to flatten it.

What is the curve?

The "curve" researchers are talking about refers to the projected number of people who will contract COVID-19 over a period of time. (To be clear, this is not a hard prediction of how many people will definitely be infected, but a theoretical number that's used to model the virus' spread.) Here's what one looks like:

A sample epidemic curve, with and without social distancing. (Image credit: Johannes Kalliauer/ CC BY-SA 4.0)

The curve takes on different shapes, depending on the virus's infection rate. It could be a steep curve, in which the virus spreads exponentially (that is, case counts keep doubling at a consistent rate), and the total number of cases skyrockets to its peak within a few weeks. Infection curves with a steep rise also have a steep fall; after the virus infects pretty much everyone who can be infected, case numbers begin to drop exponentially, too. 

The faster the infection curve rises, the quicker the local health care system gets overloaded beyond its capacity to treat people. As we're seeing in Italy, more and more new patients may be forced to go without ICU beds, and more and more hospitals may run out of the basic supplies they need to respond to the outbreak. 

A flatter curve, on the other hand, assumes the same number of people ultimately get infected, but over a longer period of time. A slower infection rate means a less stressed health care system, fewer hospital visits on any given day and fewer sick people being turned away. 

For a simple metaphor, consider an office bathroom. 

"Your workplace bathroom has only so many stalls," Charles Bergquist, director of the public radio science show "Science Friday" tweeted. "If everyone decides to go at the same time, there are problems. If the same number of people need go to the restroom but spread over several hours, it's all ok."

How do we flatten the curve?

As there is currently no vaccine or specific medication to treat COVID-19, and because testing is so limited in the U.S., the only way to flatten the curve is through collective action. The U.S. Centers for Disease Control and Prevention (CDC) has recommended that all Americans wash their hands frequently, self-isolate when they're sick or suspect they might be, and start "social distancing" (essentially, avoiding other people whenever possible) right away. 

To comply, many states have temporarily closed public schools, and many businesses have advised employees to work from home if possible. On March 15, the CDC advised that all events of 50 people or more should be canceled or postponed for the next eight weeks. On Monday (March 16), six counties in the Bay Area — encompassing some 6.7 million people — gave "shelter in place" orders, meaning that people should not leave their house except to get essentials like food or medicine. 

So, does flattening the curve work?

It did in 1918, when a strain of influenza known as the Spanish flu caused a global pandemic. To see how it played out, we can look at two U.S. cities — Philadelphia and St. Louis — Drew Harris, a population health researcher at Thomas Jefferson University in Philadelphia, told NPR.org.

In Philadelphia, city officials ignored warnings from infectious disease experts that the flu was already spreading in the community. The city instead moved forward with a massive parade that gathered hundreds of thousands of people together, Harris said.

"Within 48, 72 hours, thousands of people around the Philadelphia region started to die," Harris said. Ultimately, about 16,000 people from the city died in six months.

In St. Louis, meanwhile, city officials quickly implemented social isolation strategies. The government closed schools, limited travel and encouraged personal hygiene and social distancing. As a result, the city saw just 2,000 deaths — one-eighth of the casualties in Philadelphia.

The city, now known for its towering Gateway Arch, had successfully flattened the curve. 

Originally published on Live Science.

  • xingtukker
    Sweden decided on March 12 to flatten the curve by testing only healthcare workers and risk groups. Curve shows no cases or deaths outside these two groups and lies below the system capacity. This is a new method that protect elderly and let young fight virus on their own without healthcare support. Ofcourse even the young ones with infection can call helpline an hour before dying to tell them the curve is flattened. Norway adapted the same strategy on March 13. It all started with UK PM talk on the herd immunity and flattening the curve. Politicians gamble to agree on strategies that show less numbers.
    Reply
  • SaltyTubers
    Sooo, I have a question. I get that distancing ourselves will slow the spread, but it will not cure the virus.

    What happens AFTER the distancing and curve-flattening? Won't it just take one sick person to then infect all those that did not recover from the virus previously? Are we assuming that a vaccine would be available by then?
    Reply
  • Doogie
    From what I understand, one of the big problems with viruses like this one is not that everyone will get it, but that everyone gets it at nearly the same time. Hospitals can only treat so many people at once, and if they're short on resources (like ventilators), they need to start making decisions about who should get treatment. That seems to be what's happening in Italy right now.

    Flattening the curve basically spreads the pandemic out over a longer time so that the healthcare system doesn't get flooded.
    Reply
  • Trevor Scanlan
    Flattening this curve and closing the schools were helpful due to the sum of about 300 kids just in the highschool alone and the fact that they would be around there family and their parents were around other co workers this was a recipe for disaster so by social distancing and other practices to quarantine was helpful and healthy.
    Reply
  • DJ Wordsmith
    Flattening the curve will work as the basic premise is simply to slow the spread so the number of people needing hospital care remains below that countries ability to provide it. There are enough resources for us all to be hospitalized once in our lives, but there isn't enough for us to all do it today.

    But how to get people to socially distance so we actually flatten the curve. It's social programming, we need news articles, facebook memes, chats with friends, etc. Because that's what it'll take to completely change our habits in time to actually take effect.

    One more tool in the arsenal is to broadcast the message with shirts, bags, phone cases etc. to remind people. These products all saw "If you can read this you're getting to close" and have a stylized graphic of flattening the curve to help remind us all. Every bit helps. Stay safe! www.flattenthecurvenow.com
    Reply
  • LEON NITRAM
    admin said:
    Why slowing the rate of infection, or 'flattening the curve,' is so important to reducing the incredible damage of coronavirus.

    Coronavirus: What is 'flattening the curve,' and will it work? : Read more
    FLATTENING THE CURVE OR I COULD SAY SLOW THE SPREAD OF C-19 UNTILL WE GET SOME SOCIAL MODEL ORGANIZED AND CHEMICALS THAT WILL SLOW IT DOWN SO WE CAN GET A VACCINE IN PRODUCTION WHICH WILL TAKE UP TO A YEAR, BUT WE HAD THE Black Death AND FOUND OUT IT SPREAD MAINLY THROUGH THE RAT INFESTED SURERS IN EUROPE AND THROUGH THE DEAD BODIES BUT THEY STARTED TO CLEAN THEMSELVES AND CLEAR OUT THE RATS AND BURN THE BODIES IE THEY FLATTENED THE CURB AND WHERE ABLE TO CLEAR THE Black Death OUT AND LIFE WENT ON BUT AFTER THESE THINGS EVEN CORONAVIRUS LIFE WILL BE A SMALL BIT DIFFERENT IT MIGHT EVEN MAKE US MORE AWARE OF OUR NEIGHBOR THAT CANT BE BAD.
    Reply
  • Thomas
    This reminds me of "The Blob" (one of Steve McQueen's first films.), except that this "Blob" is all but invisible, and the whole nation is waiting for it to show up. It seems like with the current data available, this may end by the end of Summer 2020. I guess we will all find out!
    Reply
  • timtak
    There is research on curve flattening in the 1918 pandemic that which found that social distancing did flatten the curve, but total deaths were reduced by only (?) about 20%.
    https://www.pnas.org/content/pnas/104/18/7582.full.pdfI am not connected with medicine.
    Reply
  • MnM
    admin said:
    Why slowing the rate of infection, or 'flattening the curve,' is so important to reducing the incredible damage of coronavirus.

    Coronavirus: What is 'flattening the curve,' and will it work? : Read more
    Reply
  • MnM
    We need a complete curve to get the best answer. the curve should include the total number of tests that are given. Hence answer this question first and include it in the curve: How many people have tested negative for coronavirus in the united states?
    Reply