In the midst of worsening news about the worldwide spread of COVID-19 (Coronavirus), “social distancing” has become the watchword. But what is social distancing, how does it work, and how much can it potentially help slow the spread?
What Is Social Distancing?
Technically speaking, quarantines are a form of social distancing. In its simplest form, social distancing is putting enough space between yourself and other people that their “airborne droplets” from coughs or sneezes literally can’t reach you.
The specific ways to do this are totally varied by context. Here’s a list the Centers for Disease Control and Prevention (CDC) gives for people in care and assisted living facilities in particular:
Implement social distancing measures:
» Reduce large gatherings (e.g., group social events)
» Alter schedules to reduce mixing (e.g., stagger meal, activity, arrival/departure times)
» Limit programs with external staff
» Consider having residents stay in facility and limit exposure to the general community
» Limit visitors, implement screening
So far, measures in the U.S. have been “voluntary,” with event cancellations on a case-by-case basis, even at the city government level. A St. Louis-area family that promised to self quarantine decided to just go out to large events instead, and only after that are they being threatened with a court-ordered quarantine. Social distancing only works if a lot of people do it, and some places don’t think a recommendation is enough.
New York governor Andrew Cuomo announced today that gatherings over a certain size are outright banned, and intriguingly, he’s reducing the legally allowed capacity of smaller venues by half. This is social distancing in its purest form: literally reducing how many people can go in to begin with.
We are taking new actions to reduce the density of people across the state.— Andrew Cuomo (@NYGovCuomo) March 12, 2020
Starting Friday at 5pm, gatherings with 500 people or more will not be permitted in NYS.
Additionally, for facilities with an occupancy of 500 or fewer, we are reducing the legal capacity by 50%.
But will it actually work?
Mathematical Epidemiology at a Glance
These are hard questions, and we want to be clear that discussing them is speculation. That’s true at all levels of expertise, too. In an National Institutes of Health (NIH)-hosted 2013 paper, researchers specializing in mathematical epidemiology explained why. Despite rapidly advancing technology and the simple fact that we now understand what causes disease better than ever before, the problem is still far too complex.
“Unfortunately, the odds are that in a real crisis, even if researchers succeed to come up with a vaccine tailor-made for an emerged virus strain, it is doubtful that it would stop a pandemic," the researchers wrote. "The complex multi-scale interplay between a host of factors [...] imposes a real impediment to our control strategy potential.”
As with the simple math you learn in a classroom, every variable you add makes the problem more and more complicated. Eventually, it’s too complicated to ever solve in a satisfying way.
But that’s never stopped scientists from continuing to try, or from doing their best to help prevent disease and death. Daniel Bernoulli—yes, that Bernoulli—developed one of the first epidemiological math models in the late 1700s. Since then, experts in statistical methods and then regression analysis in particular have added more shades to descriptive and prescriptive models.
These methods are often what’s at play when a government or organization officially “declares” a health crisis. The mathematical threshold must be met, according to a definition everyone understands that’s based on parameters like transmission rate and number of identified cases.
In 2010, public health psychologist Lynn T. Kozlowski and colleagues published a paper on their observation of how students at their University of Buffalo responded to “voluntary” social distancing measures during the 2009 H1N1 influenza pandemic. The scientists specifically cited the idea of rites of passage like family weddings and graduations exerting a strong enough sway that people chose to ignore public health recommendations. And, of course, the sunk cost fallacy pushes people to do even stupid things they’ve already paid for.
From the researchers:
“Outright bans on handshaking may be more effective than asking individuals to decide for themselves whether or not to shake hands. In the graduation situation, an announcement that handshaking would not be part of the graduation ceremony would alter the ‘script’ for the highly ritualized situation, where behaving ‘correctly’ according to the ritual is important.”
This is true in the anecdotes people shared with writer Anne Helen Petersen, who wrote about the challenges in persuading older relatives to actually adhere to guidelines. Petersen shares one woman’s experience trying to talk elderly family members out of traveling for a funeral: “‘There’s a general attitude that we are making a big deal out of nothing,’ Nichole said. ‘A lot of “we deal with the flu every year.”’”
Decoupling this association could be vital as the U.S. makes decisions about public behavior. Yascha Mounk wrote at The Atlantic earlier this week that China’s swift action became a game changer:
“Before China canceled all public gatherings, asked most citizens to self-quarantine, and sealed off the most heavily affected region, the virus was spreading in exponential fashion. Once the government imposed social distancing, the number of new cases leveled off.”
Mounk also explained this is based on official reporting by the Chinese government. Singapore, which is ostensibly democratic but has had the same single political party since the 1950s, also responded swiftly:
“In Singapore, the government quickly canceled public events and installed medical stations to measure the body temperature of passersby while private companies handed out free hand sanitizer. As a result, the number of cases has grown much more slowly than in nearby countries.”
In a March 6 report, the World Health Organization (WHO) said that to the best of anyone’s knowledge, COVID-19 is not “shed” (spread) by people who are infected, but not symptomatic yet. That makes intuitive sense: If the virus is spread by droplets, but you aren’t coughing yet, then the risk of exposing others by more passive kinds of droplet contact does seem really really low. But that information may change as scientists have more time to study the pathogen, and we don’t want to assume anything.
Another undeniable fact: People in the U.S. are continuing to go to work when they themselves are sick or when their coworkers appear to be sick, because without paid leave, they literally can’t afford not to. In Maslow’s hierarchy, food and shelter are the basis on which the largely abstract idea of even a virulent plague rests. The optimism bias leads us to believe our odds of future survival and success are better than they are, making it easier to explain away a decision to keep an ill-advised coffee meeting or keep going to work even for people who don’t need to keep going.
So, with all that in mind, let’s look at some numbers and think about social distancing.
The Math of Social Distancing
One of the major numbers assigned to any contagious pathogen is its transmission rate. Individual people have different expressions of this transmission rate, simply because someone who stocks the salad bar at your grocery store is around hundreds or thousands of people every day, while, say, a writer who works from home might encounter just a handful. Here’s the formula for the first part, the reproductive ratio:
R = C × P × D
In the formula, C is the average number of people an infectious person comes into contact with each day. P is the probability the infectious person will transmit the virus to any particular person. D is the duration of infection. This is why, demonstrated mathematically, someone who is quarantined is absolutely not passing the virus to anyone. It’s the only parameter that can be zeroed out.
This is also where social distancing comes into play, because “contact” doesn’t mean everyone you smile at or wave to—it’s linked with the specific way this particular virus is transmitted. How many people are close enough to you that they’d receive it if you coughed, maybe even if you coughed into your elbow? How many people do you hug or kiss each day?
With the reproductive ratio in mind, now we need the serial interval. This is the length of time between when the virus is transmitted to a new patient and when that patient shows symptoms. Researchers have said, so far, that the median serial interval is between 4 and 4.5 days. But Johns Hopkins University just announced that the incubation period of COVID-19 is just over 5 days, meaning an infected person is taking 5 days to show symptoms. This contradicts a working idea that only symptomatic people are contagious, and the U.S. has, before now, refused to test people who don’t show symptoms yet because of the scarcity of available tests.
The transmission rate is the reproductive ratio combined with the serial interval. The same reproductive ratio, but with two different serial intervals, can have very different outcomes.
In a 2017 paper about the sexually transmitted zika virus, experts explained that the median serial interval was 15 days, but the Dutch government had released guidelines that people use condoms for two months, based on the maximum known serial interval of 44 days. For now, the number models released by Johns Hopkins and others show that 97.5 percent of cases of COVID-19 coronavirus express symptoms within 11.5 days, meaning the two-week quarantine period in use right now is effective almost all the time.
Flattening the Curve
Have you heard about “flattening the curve”? Public health scholar Matthew McQueen wrote an explanation of this idea and why it’s the world’s best chance to minimize the impact of COVID-19 coronavirus. “Rather than letting the virus quickly rampage through the population and burn itself out fast, the idea is to spread all those infections out over a longer period of time,” McQueen explained. We do this by reducing the only mathematical parameter we can control, which is the number of people who are exposed to the virus.
Even if everyone on Earth had paid sick leave and access to effective masks and hundreds of other hypotheticals, we could likely still not reduce the exposure to true zero. But even small changes on an individual scale mean a big difference in the full scope of healthcare.
Think of all the people who might still attend a big concert or the gigantic construction convention happening in Las Vegas right now. Every person who walks into a convention with 100,000 other people has immediately sent their contact factor and their overall viral reproductive ratio into the stratosphere.
Acting conscientiously to reduce risk has a severalfold effect on improving outcomes. First, it’s true that the vast majority of people who catch COVID-19 will recover, but many will require at least some healthcare to get there. Any reduction in simultaneous cases means more healthcare resources per case, which improves outcomes. Second, even if a minimum level of contagion is inevitable, postponing as many cases as possible for as long as possible means more people will have more access to improved testing and treatment. If a vaccine is developed, more people will benefit from it.
The third vital factor here is the fatality rate from this virus, which will creep higher as healthcare resources are stretched thinner and thinner. The fatality rate is believed to be about 3.5 percent as it stands, but up to 20 percent of people will require medical intervention. Moderate cases of the virus, when people require treatment to stay hydrated or to support their breathing, need to have resources in order to ensure a good outcome. Lives are at stake, like in Italy, where over 10,000 known cases have the attention of every healthcare worker in the nation. The decisions these providers face are grim, and we have an opportunity to try to avoid it.
Yascha Mounk’s recommendations are succinct:
“Do you head a sports team? Play your games in front of an empty stadium. Are you organizing a conference? Postpone it until the fall. Do you run a business? Tell your employees to work from home. Are you the principal of a school or the president of a university? Move classes online before your students get sick and infect their frail relatives. Are you running a presidential campaign? Cancel all rallies right now.”
The Atlantic has a more detailed guide to social distancing, too. Yes, writer Kaitlyn Tiffany says, there are different situations and levels of caution. Yes, the most healthy people have the least worries, although they’re morally obligated to act with caution to protect the most vulnerable people. And even so, “while young and healthy people who are at lower risk for personally suffering severe illness from the coronavirus don’t have to be locking themselves in their homes for the next month, they do need to dramatically alter their daily lives, starting now,” Tiffany concludes.
Think about what it means to leave a buffer of at least six feet between you and other people. It might be fairly easy to do that if you have a job with your own office. Taking walks outside is probably fine. Every time you consider your routes and activities and make some spatial estimates in your mind, you’re reducing the likelihood that you’ll be exposed or expose others.
Of all the decisions to have to make, this one is very simple math.
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