COVID-19: Wisconsin's Model

Data and modeling have been critical tools to stop the spread during the COVID-19 pandemic. We used this vital information to create policies like Safer at Home. We are sharing our data and modeling to better inform the public of the information we used to make these decisions and explain why guidance like physical distancing is so important to protect the health and safety of Wisconsinites.

What our model predicts

Our initial model indicates that, without action, COVID-19 would cause 22,000 infections by April 8 and between 440 and 1,500 deaths. These projections are based on data compiled by DHS between March 3 and March 15, 2020. This data showed exponential growth; cases doubled every 3.4 days. To illustrate this across one week, if a Monday morning started with 100 cases, then there would be 200 cases by Thursday afternoon and 400 cases by the following Monday.

Cumulative total COVID-19 cases by date confirmed

Due to the time that passes between transmission, symptoms, and a test result, policies like Safer at Home will need more time to result in a significant decrease in cases reported. This means Wisconsin’s peak will most likely occur within three to seven weeks (between April 23 and May 23, 2020).

Our updated model indicates:

  • The simulations predict that Wisconsin’s interventions (school closing, Safer-At-Home order) are having an impact.
  • The timing of a substantial late peak will be determined by the lifting of the Safer-At-Home order and comprehensive testing. Our scenarios all show that Safer at Home needs to include follow-up testing and isolation. Without follow-up testing and isolation there will be a substantial peak that would outpace our health care system’s capacity.
  • The intervention scenarios suggest that we should think of our outbreak in terms of two plans: a plan for acute challenges to hospital capacity and a plan to suppress or mitigate a second wave. Safer at Home has been our plan to address acute challenges to hospital capacity (the first phase of our COVID-19 response) and the Badger Bounce Back plan will enable us to mitigate the second wave.
  • The outbreak will strain Wisconsin hospital capacity during April.
  • Comprehensive testing is an important tool for suppressing or delaying the substantial second wave. With comprehensive testing and isolation, the magnitude of the number of cases in Wisconsin will be below the threshold of hospital capacity. 

How we created our model

Other countries currently affected by the COVID-19 pandemic, such as China, Italy, France, and Germany, have made their data available for study. In addition, many states have been impacted earlier than Wisconsin, and the information coming out of those parts of the U.S. has also proven helpful. We developed our initial model using data from the Wisconsin Electronic Disease Surveillance System (WEDSS). We calculated the growth rate of the number of COVID-19 cases that were confirmed by a laboratory test. Using the data on Wisconsin cases in the first two weeks of March as the foundation to build on, staff at DHS were able to integrate the information provided by other parts of the world to produce our current model. Our original model predicted, based on actual Wisconsin experience, that there would be 1,200 positive cases by March 25. Wisconsin actually observed 1,834 positive cases by March 25. While the test results came in after March 25, the positive cases experienced symptoms of COVID-19 by March 25.

For our updated model, our data scientists analyzed six scenarios representing the impact of interventions on Wisconsin’s COVID-19 outbreak, based on methodology developed by Johns Hopkins University Infectious Disease Dynamics group. We also analyzed the Washington Institute for Health Metrics and Evaluation (IHME) COVID-19 model, as well as consulting with University of Wisconsin COVID-19 teams and looking at various data points related to Wisconsin’s COVID-19 outbreak. The goal of our updated model is to extract information useful for making decisions about policy and resource allocation.

Why our model is important

Policies like Safer at Home and physical distancing are changing the daily lives of Wisconsinites. Our initial model explains why these policies are so important—why enacting them early in the pandemic was key and why following the guidelines is going to save lives. Because while our model indicates potential cases of COVID-19 in Wisconsin, it is important to remember that each case represents a person—a friend or family member, a neighbor or co-worker, a fellow resident of this state. Guidelines like washing hands for 20 seconds, physical distancing, and limiting trips outside the home to essential needs will save lives. These actions will flatten the curve, making it possible for the Wisconsin health care system to respond to the COVID-19 pandemic. Keeping our health care system from becoming overwhelmed so it can care for us during this epidemic is our number one priority. The science and the data tell us that staying at home is effective. The more we all stay Safer At Home the sooner we can get through the worst of this.

Our updated model tells us that it is now time to move from our initial response to COVID-19, which has been to keep all Wisconsinites at home to prevent spreading this disease. Once we reduce the transmission of COVID-19 to an acceptable level and meet the Badger Bounce Back plan criteria, we can begin to allow people to interact, and more importantly get Wisconsinites back to work. We are executing  a plan to aggressively test people for COVID-19, properly isolate people who test positive, and quarantine their close contacts. The shift we are making is from “boxing in” all the people to “boxing in” the virus.

What comes next: The Badger Bounce Back Plan

Modeling studies conducted by Imperial College London and the University of Washington indicate that physical distancing measures like the ones in Safer at Home may be needed for several months. In order to lift physical distancing, Wisconsin’s public health system must be prepared to follow up with isolation of any new cases to prevent new chains of transmission. In the event that we experience exponential growth again, physical distancing measures may have to be put back in place. This is referred to as an “on/off strategy” and is promoted by modelers at Imperial College.

Our public health experts and government leaders continue to closely monitor the spread of COVID-19 in communities across the state and other key data like people who get COVID-19 and people who die because of COVID-19. Our goal is to avoid exponential growth of COVID-19 like that experienced in New York City, Italy, and Spain, which would have profound impacts not only on patients and our health care system, but also on our economy. In less than a month, the virus has spread to every country on the planet. It’s a good thing that COVID-19 has not yet reached every part of Wisconsin, and the best thing that we can do to try to keep it from getting to every county is to keep staying at home.

We recognize that staying at home may be frustrating if you live in a community or county where no one has tested positive for COVID-19. However, the best thing that you can do for yourself, your family, and your community is to keep staying at home. It helps keep you and your community healthy and safe, and it also helps protect the capacity of your community’s hospitals and health care system.

Turn the dial for the Badger Bounce Back: Wheel with red to green circles with: Safer at Home, Access to testing, Expanded tracing, Aggressive tracking, Access to more PPE, Increased capacity, Badger Bounce BackIn order to turn the dial on Safer at Home and supercharge the Badger Bounce Back plan, we must have access to more testing and labs, expand contact tracing, aggressively track the spread, have access to more personal protective equipment and supplies, and increase health care system capacity.

None of these steps is possible without the others.

  • Positive lab tests require timely contact tracing to be sure people quarantine when ill.
  • Personal protective equipment is required to conduct lab tests and to protect health care workers.
  • Tracking the spread of the disease is required to understand our health care needs.

We want to take steps forward, and we will work diligently and as quickly as possible. At the same time, if one part of this plan takes a fall, every part takes a step back.

Last Revised: November 18, 2020