March 4, 2020 at 4:04 pm

# The Coronavirus Number to Watch is R-Zero, Says Math Expert

When Ohio University multimedia Journalism student Taylor Bruck interviewed experts from different disciplines across campus to find out more about the topic of the novel coronavirus in today’s headlines, Dr. Winfried Just was there to look at how mathematical modeling helps provide an analytical tool for assessing prevention strategies and the spread of a disease.

Just, Professor of Mathematics, is an expert in mathematical epidemiology, in particular, behavioral epidemiology. His research focuses on the possibility of future flare-ups of an epidemic due to waning awareness. Just discusses the ways in which mathematical models can predict the spread of infectious diseases like coronavirus. He says of mathematical research around disease, when compared with other research disciplines, “They study the trees. We make them see the forest.”

#### ‘What Is Going to Happen If We Do This or That?’

“What I’m doing is mathematical modeling,” Just says, “where you have essentially a simulated outbreak that you can study in the computer or with mathematical tools, and that let’s you predict what happens given the current knowledge about the disease. What is going to happen if we do this or that, or not do this?

“So the most important question here is how prevalent will this be? How many people will experience infection during the outbreak until it’s over? And that’s the kind of thing we can predict with these mathematical models without actually exposing people to risks,” Just says.

#### R-zero—the Number to Watch

“The most important number in disease modeling is what we call R-zero. And R-zero is actually easy to understand. It’s the average number of people that will be infected by an infectious individual. And that R-zero is something that helps us predict how many people ultimately will get infected. For the coronavirus that’s right now on our minds, we don’t know what it exactly is. There are estimates that range from R-zero is equal to 1.4 to 3.9, according to today’s information,” Just says.

“And this is where the other sciences come in—psychology, media studies, sociology, biology—they get us to the place where we can narrow this down. So if we have an outbreak with an R-zero of 1.5, then we would predict that almost 60 percent of all people would experience infection. If the R-zero is like 2, then we would predict about 80 percent becoming infected eventually…. If the R-zero is something like 1.1, then we would predict about 17 percent of the population infected. It is still big.

Dr. Winfried Just

“However, if the R-zero gets below 1, then we are safe. Then we will have some infections; some people will die. That is regrettable, but we will not have this kind of major outbreak where a sizable proportion is infected.”

The R-zero that is being currently estimated is “under the assumption that nothing will change,” Just notes.

“If people change behavior, if they change their contact pattern, then we can decrease this R-zero, and hopefully below that threshold of 1, where the outbreak will just peter out. And we were successful with that with the SARS outbreak. ”

Among the changes Just suggests common “control measures” will affect the spread of infection: