The SIR Flu Model

Ask your teacher if you will be using the Stella model or the Java version.

If you are using the Stella model set these initial conditions:

If you are using the Java model set these initial conditions:

These values create a population of 1001 people. At the beginning of the run only one person is sick. Sick people can spread the flu for 3 days on average.

To see the numerical data on the Java model click the text output button. That opens a window with 4 columns of numbers. The first column is the day. The second column is the number of contagious people. The third column is the number of recovered people. The fourth column is the number of susceptible people. You can copy and paste this data into an Excel spreadsheet.

To see the numerical data on the Stella model, click on the graph. Values appear for each variable. As you drag the cursor across the graph you can see the values for different days. If you open the Table 1 icon a table of the data appears. This data can be copied and pasted onto an Excel spreadsheet.

Consider the formula that moves people from the susceptible stock to the infected stock. People moved = susceptible*contagious*infection_rate. The infection rate = the virulence factor / total population. Thus the full formula is People get sick = susceptible*contagious* virulence factor / total population.

Use the "get sick" formula to explain the change in the contagious stock.

Models allow you to explore different scenarios.
How would the flu spread if a bus full of sick people came to town? Use the contagious slider to systematically evaluate the effect of changing this variable.

Epidemiologists have studied flu outbreaks. The following data shows the percentage of people that stay home by the third day of the flu.

Employers have policies on sick leave. Some companies only pays people who come to work. If you are sick and stay home you don't get paid. Other companies give their employees 2 weeks of paid sick leave. They are telling their people, "If you don't feel well, stay home so you don't make us sick!" By changing the sick leave policy the employer can change the percentage of people that stay home when sick.

This model keeps track of the lost productivity due to illness. If people stay home sick, the company loses one day of productivity. If employees work when they are sick they get less work done. The model calculates a 30% reduction in productivity for each day worked by a sick person. A person is sick for 7 days in the simulation.

Adjust the "days contagious" slider to simulate different sick leave policies. The "lost productivity" graph displays the number of work days lost.

In the above scenario everyone followed the incentives of the sick leave policy. A real community has different employers, school children, retired people etc.

The model can simulate people getting flu shots. Your company wants you to recommend a vaccination policy. Flu shots cost $10 per person. A day of lost productivity cost the company $100. The employees of your company are 10% of the community. Employees call in sick when their children are sick. Employees and their dependents make up 30% of the community.

Your job is to determine if it would be cost effective to vaccinate some or all of the employees or the community.

Instructions for simulating vaccinations using the Java model:
Adjust the recovered and susceptible sliders. Example, for a 10% vaccination rate set the recovered to 100 and the susceptible to 900. Then run the model.

Instructions for simulating vaccinations using the Stella model:
Adjust the vaccination rate slider. Example, for a 10% vaccination rate set the slider at .10.

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