What Does 'Slowing Down' The COVID-19 Curve Mean?

Mar 16, 2020

Epidemiologists and public health experts around the globe are advocating measures to slow down COVID-19's spread, like unneccessary travel, washing hands and continuing the act of social distancing.

As the number of cases nationwide of COVID-19 has surpassed 3,400, as of Monday afternoon, President Donald Trump and Vice President Mike Pence recommended Americans cancel any meetings with more than 10 people. 

The spread of the virus is determined by a number of factors, illustrated in an equation public health experts refer to as reproductive number or (R0). This is why you've heard many of them say "reducing the curve" or "slowing down the curve" of this cornavirus. But what does mean? 

Dr. Aileen Marty is a physician in the fields of infectious disease and disaster response at the Florida International Uuniversity's Herbert Wertheim College of Medicine. She led the U.S. response to the Ebola outbreak in Africa and was critical personnel in containing the spread of the Zika virus in South Florida. Dr. Marty joined host Luis Hernandez to talk about COVID-19 and what people can do to stop the spread. 

This excerpt below has been edited ligthly for clarity.

WLRN: What does 'reducing the curve of the virus' mean?

MARTY: We measure the rise of cases, that's that curve, and we compare what that rise of cases is. With the rise of this infection that rise is very steep and that means a lot more cases, a lot more use of ICU space and a lot more deaths. If we flatten the curve, that means that we're employing those tools at our desk position in order to get the total number of people that get infected to be lower, bring it down, and also that the numbers per unit time get lower so that we can manage whoever does get sick and that we don't run out of equipment, beds and everything else.

What was China doing to bring down that curve?

China did not wake up to the reality that they had a massive problem until the end of December, at which point they realized that they needed to follow the international health regulations, which every country, including the U.S., that's a member state of the United Nations signed, which explains what each country's responsibility is for an important outbreak.

At that time, it was just an outbreak and becoming quickly an epidemic. What the Chinese decided to do at the beginning of January was to report everything they could. Basically, they published every single thing they could. They instigated the various things that have to be instigated to reduce what's called the reproductive number because the way to flatten a curve is to reduce the number of people. And that's what reproductive number is about, the number of people that get infected from each person that has the disease.

A graphic to help you understand what health experts mean by slowing down the curve.
Credit Dr. Aileen Marty / Courtesy

The Chinese were separating families and isolating them from everybody else. The Chinese method was a little draconian. But is that really the only way?

Problem is, you employ the tools you have. That's really the bottom line. If we had a vaccine, which we do not have and will not have for a year and a half, and I assure you that's very optimistic for this virus. They knew they had to use the other methods available at hand to reduce the reproductive number. And I think it might be a good time to go over what that reproductive number entails and what the different things are.

What are they?

You have an equation here. When you have a patient, a person with the virus, we look at how many people they might be infecting within that certain amount of time. What we're doing here is we're talking about the R-zero. That's the symbol that we have for the person and how many other people they're going to infect. So if you do nothing, you have an R-zero and then there are four parameters that we look at.

The first one is how long are they shedding enough virus to infect somebody else? And that's what we call the duration.

The second thing is, what is the opportunity for that person shedding virus to infect somebody else? And that means how close they are to other people and we think about that as the contact rate.

The next thing is the transmission probability. What is the probability that if I'm next to someone who has this virus, that I'll actually catch it from them? And that has to do with whether or not that person is speaking or coughing or shedding virus around the space as I am, or if I put my hand in contact with that material that somebody who has the virus has inadvertently shed and then touch my mucous membranes. And by that I mean my mouth, my nose, my eyes.

And so the fourth thing is how susceptible I am as a host to manifesting disease. How likely am I to get sick because I have that virus in my body. And so that's when we talk about how old you are and whether or not you have high blood pressure and how healthy you are.