'An Extreme Scenario': Transmission Rate Math Highlights Need For Strict Social Distancing

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Many physicians are parents, too.

And some physicians whose children go to Brookline schools say they were alarmed when they saw some guidance put out by school officials. They say the guidance was that play dates between a couple of families were OK, as long as everyone was healthy.

The doctors thought the guidelines were misguided. So they joined with some of their other medical colleagues to put out a letter of their own. It has stricter medical recommendations. They sent it to Brookline Public Schools, and it circulated to some other school districts.

One of the parents is Dr. Vandana Madhavan. She's clinical director of pediatric infectious disease at Massachusetts General Hospital. Madhavan says the clinicians felt the need to speak out about the restrictions all of us — children and adults — need to impose on ourselves.

Interview Transcript

That's the focus — that we really need to make sure this is properly contained and mitigated, because we know that there is such a large number of the population at risk.

Lisa Mullins: Let's get to the letter that you signed along with 49 other doctors. It includes a kind of table top math exercise that is quite sobering. Scientists ... measure the spread of an epidemic by calculating a couple of things. One is the way it develops in an individual, and [the other is] how many other people that individual gives it to before that person is no longer infectious, because they're either cured or they're dead. The number that doctors use is called R0, [said "R naught"]. So the R0 for the coronavirus, according to the letter, is close to three. What does that mean?

So the R0, if it's close to three — about 2.7 is the latest estimate — it means that one person with the infection, without any social distancing measures, without quarantine, without proper identification, would likely infect 2.7 or close to three other people.

And those three people are then going out to the community, interacting with others outside of the family unit. Those three people infect three more people. So that's nine more people who are infected by those three people ... Those nine new contacts then can each infect three more people. And again, this is assuming that there are no limitations being put into place and they're going around in their community. And that's another 27. Those 27 people each infect three more people. That's 81. And so each line that we've included in the letter is not a cumulative total. That's just how many more are infected in the latest ring of contacts. Without interventions to limit this ever-growing spread, the number of active cases at any one time could get so large that it overwhelms health care resources.

So you see that from the hospital's perspective. Just from a lay perspective, I mean, it's pretty jaw dropping. The letter says in just 15 steps of transmission, you can start off from one person and with with no kind of restrictions on that person's movement, within a matter of weeks, you can have that one case expand to more than 14 million people if you continue doing the math.

Right. I mean, that is clearly an extreme scenario where each person ... with a very mobile society, without travel restrictions, community restrictions, etc., it's certainly feasible for each newly infected person to have three new contacts who have not been previously exposed.

There are interventions going on, and as you say, there is social distancing going on. But the ones that you would especially highlight  — that again are recommended in this letter — the one that I think a lot of parents ... certainly kids might have trouble with [is] your first recommendation: no play dates, not even one-to-one.

And that is something, as a parent of an almost-9-year-old and 6-year-old, it's one that strikes really close to home ... You know, I would say for parents of teenagers who can be trusted to walk six feet apart from one other friend, it's one thing. It's one thing for older kids who can be trusted to take a bike ride with one other friend, again, staying that distance apart, not sharing bikes, not sharing helmets, things like that. It's very different. But the idea of a play date with unrestricted play time among even two children, it just really raises the risk of asymptomatic or mildly symptomatic spread ... And so it just should be off the table right now.

I'm going to jump now to the very last recommendation that says, 'Please avoid disseminating social media claims that the situation is not serious or that it's being exaggerated. This is a national crisis. Conveying misinformation to your friends and family may put their lives in danger.' Yesterday, President Trump suggested that there may be a way to ease up on some of the social distancing measures sooner rather than later. Do you see that as a possibility?

I don't foresee that as a possibility any time in the upcoming few weeks. We have no sense of the actual extent of infection in the U.S. because we've had such limited testing capabilities ... and without having more testing, we really have no idea of how widespread infection has already been ... And so without having that data, it is extremely premature to be able to say that we can start easing restrictions [meant] to limit [coronavirus] spread at this time.

This segment aired on March 24, 2020.

Headshot of Lisa Mullins

Lisa Mullins Host, All Things Considered
Lisa Mullins is the voice of WBUR’s All Things Considered. She anchors the program, conducts interviews and reports from the field.


Headshot of Lynn Jolicoeur

Lynn Jolicoeur Producer/Reporter
Lynn Jolicoeur is the field producer for WBUR's All Things Considered. She also reports for the station's various local news broadcasts.



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