The model explained

Hufnagel had the benefit of example, the epidemic of 2003 from Hong Kong. His goal was to simulate what actually happened. There is nothing to say that SARS or like disease would behave the same way in a country with such different properties as where it did turn up but it is a good starting point. Working with control measures enable us to produce a "comparative result" which means that the exact number of infected in our simulation is less important. What's important is to show that under all reasonable circumstances, travel restrictions reduce this number.

This would be fine for a random mixing-model of a small population but as we wanted to model all of Sweden, we duplicated it for each for the 298 municipalities. We now have a few additional factors to take into consideration compared to the original state model.

Diagram representing an "event". I means infectious, R means recovered so the diagram shows the possibility of an infectious infecting someone else or recovering. The choice is made randomly, by the throw of the dice.

This diagram shows the events from the different states in a random mixing model. People move from S through L and I and finally end up in R. The probability of the random generator choosing a particular event depends on different factor. For example, the rate of people moving from S to L i.e. become infected depends on how many in their environment are infectious and also how contagious the disease is. Moving from L to I is solely a matter of incubation time, the time for symptoms to appear from the time of infection.

This diagram is similar to the previous but instead of representing the whole country, it now shows a single municipality in Sweden. What's chaned is the factors determining the rate from S to L. We're intrested mainly in the number of infectious in the municipality, Solna in this case. But also other municipalities make an impact depending on the travelintensity between the couple.

For our model we take the random mixing model and reproduce them over the whole country, one for each municipality. If there was no traveling between the municipalities we could make 289 paralell simulations. But since people do move around we have to enable the separate instances to talk to each other.

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