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WHAT IS IT?

At a very basic level adaptation is about keeping up with change in the environment. For example, does change in the response system keep up with a increase in infections? These types of questions are easier to talk about with a simple dynamic model.

My draft model simulates illness spreading, children, adults and elderly going from home to public places, with surveillance, different vaccination strategies, and agencies with the authority to close schools. It is meant to be very simple, to stimulate thinking about adaptive response.

This simple “toy” model is an early attempt to create simulations in a format that anybody can use. This format allows partners to view and modify some parameters of the simulation through a web browser. The scale of this town is very small to simplify the model. The purpose is not to predict absolute numbers of infections but rather to generate new insights into the type of dynamics at play.


HOW IT WORKS

In this draft model, you can try out different combinations of vaccination and school closing strategies.

You can set the total amount of vaccine available, and choose to vaccinate any of three demographic groups: children, adults, elderly or all three. You can set the proportion of adults and elderly that want to get vaccinated and parents that want their child to be vaccinated, the day that they go to get vaccinated, the effectiveness of the vaccine. Note that each of these three demographic groups has a different amount of contact with others (children have a high rate of contact, and elderly a low rate), and a different chance of becoming infected from any given contact.

Any of three agencies may have the authority to close school. We may authorize any or all of these agencies to close schools. So you can try turning the authority to close school "on" or “off.” Once you switch that on, kids will no longer go to school, if the threshold of sick children is large enough. Right now that slider just sets the threshold as a number of sick children.

You can have sick people stay home on the weekends, and see what effect that has on the spread of infection. You can have a certain proportion of sick adults decide to stay home from work. And you can try different combinations of all of the above, or compare different strategies and see which is most effective in mitigating the spread of infection. (Keep in mind that school closings and staying home from work are not have costs of their own).


HOW TO USE IT

After you hit the “setup” button you see homes, a school, a workplace, a park, hospital and health department appear. Children, adults and elderly populate the homes.
See people move to public places: schools, work, shops and a park. Children go to shool and have a high rate of contact. Adults go to work and have a slighly lower rate of contact. The elderly (who live the the last two homes on the right) only go to shops. You can see that the elderly have a lower rate of contact.

On the on the weekends all demographic groups go to shops and the park. There is a window telling you the day of the week, another window showing how many days have elapsed, and windows showing the spread of infection, and vaccines still available.

By default, one person is infected on day 1, but you can change that day of first infection with the slider.

You also can initiate an infection whenever you want. Hit the “infect” button whenever you want to initiate an infection. That will cause one person, at random, to be infected. Watch the infection spread. You can use the sliders to change settings. You can change the infection rate and duration.

You can give the health department the authority to close the school by switching that setting “on.” Or you can turn it off. You can add a delay to any school closing.

The model also allows you to experiment with vaccination, but if you want to look at the effect of school closure without any vaccination, then turn the vaccination off by setting the proportion of adults and children getting vaccinated at 0% (the default is 0%).

If you want to see what happens with vaccination alone, turn the school closure off, and set some proportion of adults and children going to get vaccinated. You can adjust the proportion of adults and children that go to get vaccinated (more precisely the liklihood of going to get vaccinated), the day that they go to get vaccinated, the effectiveness of the vaccine and the amount of vaccine available. Note that the vaccine can run out if the proportion of vaccine per person is less than 100%.


THINGS TO NOTICE

When there is a limited amount vaccine, you must choose which demographic groups to vaccinate. Note that the elderly may have a higher chance of becoming infected, but a lower contact rate. Note that children have a higher contact rate. Thus the children will be more effective spreaders of the disease even if the elderly are more susceptible. Under certain conditions, vaccinating children may be the most effective strategy to stop the spread of the disease. Thus even if the elderly are more susceptible and more likely to die from the disease everyone may benefit more if the disease is stopped.

You can set the total amount of vaccine available, and choose to vaccinate any of three demographic groups: children, adults, elderly or all three. You can set the proportion of adults and elderly that want to get vaccinated and parents that want their child to be vaccinated, the day that they go to get vaccinated, the effectiveness of the vaccine. Note that each of these three demographic groups has a different amount of contact with others (children have a high rate of contact, and elderly a low rate), and a different chance of becoming infected from any given contact.

Notice also that the school closure may be more complicated than we expect. Each of the three agencies (the department of education, and the emergency management agency, and the health department) might have the authority to close school. But they might have different criteria for closing down the schools. So here we have a separate slider for each of the three departments. So the user can set the department of education at a different threshold, a different number of children can get sick before the department of education’s alert goes off. Same with the emergency management agency.

Once a certain threshold of sick children is reached, the health department signals an alert. But the emergency management agency may have a different threshold. So with different thresholds we see the alerts go off successively. First the health department, then the department of education, then the emergency management agency alert. But the school only closes if the agency also has the authority to close the schools. We don’t see that happen in the movie because the authority is not switched on.

Note that school closure along may have little effect if people still go to other public places. That is, even when kids don't go to school interact in the parks and shops on the weekends, and parents still go to work. But you can have sick people stay home on the weekends (switch that on) and you can set a probability that an adult will stay home from work (between 0% and 100% liklihood). The default setting are to have sick adults stay home with a 50% probability, and have sick persons stay home on the weekends.


EXTENDING THE MODEL

The modeling program records each run along with the parameters that were set at that time. The proportion infected over time for each run is displayed as a plot and recorded. The model produces slightly different results with each run, because some randomness is built into the simulation. So we record average results over many simulation runs. That allows us to see patterns emerge over many runs, for any given settings. For example, if there is a different criterion operating for school closure authority between the education department and the health department, then delay in closure is likely to occur and more children will become infected.

You can compare interventions, or combinations of interventions, by running the simulation over and over and averaging the results for each separate intervention.


CREDITS AND REFERENCES

Authored by Christopher Keane.
Inspired by the elegant models of Josh Epstein, my mentor in modeling.