Robbie Sequeira

Ames Tribune

A team of Iowa State University researchers says a computer model it has developed shows the coronavirus continues to spread in Iowa, but that the rate of transmission has slowed since reaching a peak on March 16.

Yumou Qiu, assistant professor of statistics at Iowa State and a member of the research group, said the slowdown indicates the social distancing measures the state has taken are having an effect, but that the continued spread of the virus means the pandemic’s effects in Iowa are far from over.

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

He said that the mathematical model relies on COVID-19’s "effective reproduction number," which is the average number of secondary cases per infectious case in a population made up of both susceptible and non-susceptible people.

Qiu said if that value is above 1.0, it indicates the disease is spreading; a value below 1.0 suggests that the spread is decreasing and under control.

“Even when we start seeing declines in the value, it’s important for us to see if that number dips below that 1.0 value, which tells us that this disease is controlled,” he said.

In Iowa, the value reached its peak on March 16, when it was at 3.91. As of Friday, it was 1.65, a more than 50% decline, and had dropped as far as 1.54 on April 3.

► More: Here's the latest information on the coronavirus in Iowa

Qiu said this coincided with the first cases of COVID-19 confirmed in Iowa, in Johnson County, at a time when the state's public schools, colleges, and universities released students for spring break.

“Iowans were traveling, college students were returning home and many people were headed to and from vacation locations across the globe,” Qiu said.

He said his team tracks the COVID-19 value daily, and in doing so, it can help predict the spread in Iowa.

There are a couple of factors that affect the value, according to Qiu, including a region’s population density.

“The (value) in Iowa is different from the (value) in New York City, because New York state is more crowded, and the population is higher in those bigger cities,” he said.

The second contributing factor to the value is the state’s COVID-19 mitigation strategy. Effective policies to ensure social distancing, Qiu said, can help drive the value down. It’s been a month since Gov. Kim Reynolds issued her first statewide order mandating closures and operating limitations for businesses and schools, and implemented guidelines restricting public gatherings to 10 people or less.

While the drop in value is notable, Qiu said it is still greater than 1.0, which means COVID-19 continues to spread across Iowa, increasing new cases.

“So the decline from the peak immediately indicates that (Iowa’s) policies are effective,” he said. “But also notice that in a recent few days, we are still seeing a slight increase in numbers. These dynamics indicate that Iowa has not fully controlled the spread yet.”

Qiu estimates that there could be close to 741 undiagnosed cases in Iowa.

According to the group’s models, the value in the United States peaked at 6.1 on March 11 and currently sits around 1.1.

Robbie Sequeira covers government for the Ames Tribune. Reach him at rsequeira@amestrib.com.