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Iowa State University researchers develop their own model to forecast COVID-19

This mathematical model reveals "critical characteristics" on how contagious the coronavirus is and how quickly it spreads through populations, researchers said.
Credit: WOI

AMES, Iowa — As the state partners up with the University of Iowa to create a model to predict the spread of COVID-19 in Iowa, researchers at a rival university are doing the same.

A team of researchers at the Iowa State University Department of Statistics developed a mathematical model that reveals "critical characteristics" about COVID-19, like how contagious the virus is and how rapidly it can spread through a population.

The model calculates COVID-19's effective reproduction number (R) to reveal the reasons why Iowa cases grew from few to more than 1,700.

Research member and assistant professor of statistics Yumou Qiu said he believes this model is an "accurate and reliable way" to determine the epidemic spread of COVID-19.

"Our very detailed methods calculate those important reproduction numbers, offering rich insight into how COVID-19 behaves and impacts populations," Qiu said.

Here's how it works:

The value of R estimates the average number of people one person with COVID-19 will infect within a given population. To put it in simpler terms, R "quantifies how contagious a disease is and the speed at which it spreads." 

The models created by these researchers calculate effective R values. These numbers measure how contagious the virus is inside a population with its unique demographics, socioeconomic attributes and policies for handling the outbreak. 

An R above 1.0 shows that a disease is spreading while an R under 1.0 suggests that the spread is decreasing and under control.

“The R in Iowa is different from the R in New York City,” Qiu said. “Our models produce analysis that is pertinent and specific to each location.” 

So, what does this model say about Iowa? 

Researchers are using this model to explain and predict the spread of the virus in Iowa. The models reveal COVID-19 transmission rates and shed light on how Iowa's current mitigation efforts may be impacting the spread.

When the first cases popped up in Johnson County, the estimated R0 value was 3.45. The state's overall R value peaked at 3.91 on March 16. 

Researchers dived further into the data to determine how COVID-19 spread during the time when schools, colleges and universities released students for spring break.

“That peak, or spike, in Iowa’s R value signifies a time when there was a lot of movement and activity around the state,” Qiu said. “Iowans were traveling, college students were returning home and many people were headed to and from vacation locations across the globe.”

Iowa's current R is 1.65, a 50 percent drop since that March 16 peak. 

ISU researchers say that's good news, but with a major caveat. Qiu said that while a 50 percent drop is encouraging, the R value greater than 1 signals a "compelling reality": COVID-19 continues to spread in the state.

“These dynamics indicate that Iowa has not fully controlled the spread yet,” he said. “We estimate that there are 741 undiagnosed COVID-19 cases in Iowa, and that this week’s confirmed infections will range from 680-1397.”

Since Gov. Kim Reynolds' public health disaster emergency proclamation on March 17, Iowa's R has dropped to an all-time low R value of 1.54. That value was recorded on April 3.

The R value ticked slightly up to 1.65 on April 14. 

Over the last 10 days, Iowa's average R value was 1.66, which shows that COVID-19 is still spreading.

“We don’t know when an infection will end. Those realities are sensitive to average recovery days and future infection rates, which can change rapidly. This is a very dynamic situation,” Qiu said. 

“Social distancing has made a significant impact in Iowa to slow the spread, but Iowa’s battle with COVID-19 continues to develop and change rapidly.” 

What have the models determined on a national scale?

COVID-19's R value in the United States peaked at 6.1 on March 11, according to the research team. It now sits at 1.1. 

Although social-distancing has significantly helped the country, the research team's models predict a "worsening and prolonged outbreak for the United States."

They estimate around 165,000 cases remain undiagnosed in the country, and that 217,000-233,000 new COVID-19 infections will be confirmed this week.

Based on the data, Qiu predicts the final case numbers in the U.S. will reach 1.2 to 1.5 million.

“The R numbers continue to be very important in gauging the statewide and national spread of COVID-19,” Qiu said. 

“Our models can help policy makers determine what strategies are working and when more needs to be done to mitigate this global pandemic.” 

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