New website tracks key metric of pandemic trends in Illinois
A group of Illinois COVID-19 researchers has launched a webpage to try to help residents see and make sense of the latest pandemic trends, including one of the easiest metrics to understand: the reproduction rate.
Though it’s based on complicated math, the reproduction rate offers a simple gauge of the pandemic’s trajectory. A number above 1 means the epidemic is growing. Below 1 means it’s shrinking.
One way to think of it is that the figure represents the average number of new people who are infected by one sick person before that sick person recovers or dies.
So if 100 sick people collectively infect exactly 100 new people, the pandemic isn’t growing or shrinking. But if those 100 sick people infect 110, the pandemic is growing, with a reproduction rate of 1.1. If those 100 infect just 90, the rate is 0.9 and the pandemic is shrinking. If the rate stays below 1 for good, the pandemic will die out.
Currently, three different estimates from the modelers all show that, at last count, the pandemic was shrinking statewide, with the reproduction rate around 0.88 to 0.95. But not all regions were faring as well as others, with some hovering near a rate of 1, according to at least one team’s projection.
The site, illinoiscovid.org, is being built and maintained by researchers from Northwestern University and the University of Chicago, two of the four groups that are advising Gov. J.B. Pritzker on COVID-19 trends. The other group members — the University of Illinois at Urbana-Champaign and Argonne National Laboratory — contributed their models’ outputs, too.
The site includes much of the data that can already be found on the state’s website, such as daily case counts and testing figures. But the state site doesn’t offer the reproduction rate, known as “Rt” to researchers who study virus trends.
One of the site’s founders, Jaline Gerardin, said one goal was to offer residents Rt as a better way to gauge “how things are going” than the percentage of tests that come back positive, a commonly cited metric called the test positivity rate. Plus, she said, researchers wanted residents to get a better understanding of how the projections are made.
“We wanted to increase transparency to the public on how the models work, what they say, how modelers use them, and what kind of results we’re communicating to the governor” and the Illinois Department of Public Health, said Gerardin, a Northwestern University assistant professor of preventive medicine who works on virus modeling.
The website offers calculations by all four teams of researchers, which can vary notably because each crunches the numbers a bit differently. (Argonne calculates an Rt figure only for region 11, which is the city of Chicago. The others calculate Rt for all regions individually, as well as for the state as a whole.)
The models work by analyzing other available data on pandemic trends, then working backward to estimate whether, and how much, the pandemic was growing or shrinking at the time.
The site also contains academic papers by team members, but not the weekly reports they submit to the governor. Gerardin said they may be uploaded soon, as could data on vaccination trends.
“We’d like to add any data that we’re allowed (by the state) to share,” she said.