This model allows students to examine the effect of immunity durability on the max daily cases and epidemic duration in a population. It helps students understand why booster vaccination is needed.
Grades: 9-12; Intro Biology
Embedded Files
HOW IT WORKS
1. Susceptible-infectious-recovered (SIR) model is used to build the present model.
2. The model starts with a population of susceptible people (green) and one infectious person (orange). The infectious person carries the virus strain with the defined initial transmission rate.
3. In each tick, each infectious person produces a new virus. The virus transmission rate either stays the same or mutates to become more or less transmissible at the defined mutation rate. The transmission rates are color codes.
4. The new virus may float 0.5 steps in a random direction and infect one of the susceptible people within a radius of 1.5 at its transmission rate. The virus loses its ability to infect people if no susceptible people are within the infection radius.
5. Infectious people remain contagious for six days. They either recover (become blue) or die at a mortality rate of 10%. No new people join this model to maintain the population density.
6. Users may set up the percentage of vaccinated people in the population. The present model assumes that vaccinated people will not be infected even if viruses mutate.
7. Vaccinated and recovered people lose immunity after the time defined by the "immunity durability." This model assumes that the durabilities of natural infection and vaccine-induced immunity are the same.
8. The booster vaccination extends the immunity durability of a defined percentage of vaccinated people. For example, when immunity durability last 30 days, a booster rate of 50% will extend 50% of the vaccinated people's immunity durability for another 30 days. The unboosted people will not be boosted anymore. Therefore, vaccinated people will decrease over time if the booster rate is less than 100%.
HOW TO USE IT
First, choose the factors, such as population size, transmission rate, etc.
Click on Set up/Reset, then Run/Pause. The model is set to stop when there are no infectious people.
Observe the infection changes in the population in the plot and monitor.
Use Run one day to run the model in a controlled way and collect day-by-day data.
The people in the model are color-coded in two ways: SIR coloring and transmission rate coloring. The mode of SIR coloring displays the population based on people's health status (i.e., susceptible, infectious, or recovered); the mode of transmission rate coloring displays the population based on the virus transmissibility when the people get infected (i.e., cyan and brown indicate the people who are infected by the less transmissible strains while red and purple indicate the people who are infected by the highly transmissible strains). Use the button Switch color-coding mode or the switch Color-coding-modes to switch between the two modes.
Use the slider Immunity-durability to test how the durability of immunity affects the severity and duration of an outbreak.
Use booster-rate to test how booster rates affect the severity and duration of an outbreak.
THINGS TO TRY
Observe the prevalence of color-coded strains in the simulation window and plots to examine the prevalence of different strains over time.
Collect the data of the max daily cases and epidemic duration to examine the effect of durabilities of immunity in populations with different densities.
Collect the data of the max daily cases and epidemic duration to examine the effects of booster rates in a population.
CREDITS AND REFERENCES
CREDITS AND REFERENCES
Dr. Lin Xiang (lin.xiang@uky.edu) created this model at the University of Kentucky in 2023. If you mention this model in a publication, we ask that you include the citations below.
Xiang, L. (2023). Infectious Disease Outbreak-Immunity durability and booster vaccination. Department of STEM Education, University of Kentucky, Lexington, KY.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/4.0/.
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