The research of a retired Iowa mathematics professor has taken on a new level of relevance during the COVID-19 pandemic.

Herb Hethcote became a pioneer in building mathematical models to track the spread of infectious disease during his 37-year career at Iowa. He published 73 papers showing how models can predict the spread of viral disease and how to reduce it. Those studies have been read hundreds of times a week since the COVID-19 pandemic began in March 2020, and received more than 1,800 citations in other scholarly papers in 2020 alone.

“Starting in 1970, I formulated and mathematically analyzed many mathematical models for infectious diseases in homogeneously mixing populations and determined thresholds for different behaviors,” he says. “Then I analyzed models with increasing complexity, such as multiple interacting groups, variable population sizes, age structure, nonlinear incidence, and delay-differential equations.”

After developing the theory, he started using infectious disease modeling to study specific diseases such as gonorrhea, HIV/AIDS, measles, rubella, chickenpox, shingles, whooping cough, influenza, and smallpox. His insight, he said, was to study the interaction of infectious people who interact with groups of people who are susceptible to infection. He says it’s not unlike the impact one kind of molecule has on other types of molecules it comes in contact with.

The paper that’s been most frequently cited is “The Mathematics of Infectious Diseases,” published in 2000 in the SIAM Review by the Society for Industrial and Applied Mathematics. The work has been cited more than 5,500 times since it was published, many of them in the last year. Hethcote says the paper is essentially a how-to manual for building a mathematical model for infectious disease transmission, so it’s especially relevant during a pandemic.

“It’s a short course in building a mathematical epidemiological model,” says Hethcote. “It shows how to build a simple model that researchers can build from.”

Hethcote isn’t sure who has been using his discoveries over the past year. He suspects many are researchers building models as part of their work related to COVID-19, but he wouldn’t be surprised if some were just curious about models and epidemiology.

Hethcote, 79, joined the Department of Mathematics faculty in 1969 after receiving his doctorate from the University of Michigan. He and his wife, Leslie Marshall, a professor in the College of Nursing, retired in 2006 and moved to Bainbridge Island, Wash., where they continue to live.