Level 1
Introduction
Infectious diseases are illnesses that spread from person to person through bacteria or viruses. Scientists use computer models to simulate how infectious diseases spread in a human population. These simulations allow scientists to predict what may happen in the future, and to run virtual tests of treatments to reduce the spread of disease. The simulations in Go Viral are meant to help you learn the basic concepts of how viruses spread, but the specific numbers do not reflect a particular disease.
In Level 1, we will simulate infectious disease with a classic computer model of infectious disease called the Susceptible-Infected-Recovered (SIR) model. This model assumes there are three groups of people:
(S)usceptible people are healthy, but they may get the disease from Infected people.
(I)nfected have the disease and can spread it to Susceptible people.
(R)ecovered people were infected but have since recovered.
The model also assumes that once a person is Recovered, they cannot be Infected again.
What is a computer model?
Computer models help us test our understanding of how that system works. We learn from computer models by using a “guess-and-check” approach. Guess what will happen if you change something about the simulation, then run the simulation and see what happens. If you’re right, great, it shows you may understand that part of the model. If you were wrong, that’s ok too- it focuses your mind on the parts you need to understand better and will help you make a better guess next time.
Simulating the spread of infection
Go to the Infectious disease simulator here: https://scratch.mit.edu/projects/375763600. Click the green flag to start the simulation. The simulator will add people to the screen. As shown below, most people will start as Susceptible (yellow), but a few will start Infected (red).
The graph in the lower left shows how the number of Infected people changes over time. As the simulation continues, you should see the Infected people eventually become Recovered and the number of Infected will decrease.
When Infected people touch Susceptible people, we will often see the Susceptible person become Infected. This leads to a large increase in the number of Infected people. Eventually, the Infected become Recovered, which decreases the number of Infected.
Discussion Questions
Repeat the simulation several times. Why did some simulations lead to many infections, while other simulations predicted fewer?
Based on what you see in the simulations, what changes do you think would most slow the spread of disease?
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