We often hear reference to modelling done in universities or research centres. This modelling is important because it is the basis of important policy decisions.

This is a Dummies Guide to help the curious understand one of the more simple methods used to build these models. The model has a simple set of images that represent the computer code that drives the model. It is a computer simulation model using System Dynamics.

The model is of an Australian state with an adult population of 5 million people. The vaccine is a two-dose vaccine. The government is ordered 500,000 doses each month for two years and prioritised the first dose.

To start, it helps to think of a series of bathtubs filled by a series of pipes which are controlled by a series of taps. Each series of bathtubs contains stuff: in our case: people and vaccines,

The Dummies Guide model for a vaccine rollout using this system would start out looking like this. The members of the unvaccinated population receive their first jab and move on to the population with a first jab. Some remain behind in the unvaccinated population. Members of the Population was 1 Jab receive a second jab and move on to the population with two Jabs.

The Unvaccinated Population flows into the population with 1 Jab through the flow entitled First Jab. The same dynamic applies to the population with the Second jab.

This is possible because of another associated Co-flow. There Is a supply of Vaccines. They accumulate in a warehouse or vaccination hub according to the demand generated by the first and second jabs..

The government endeavours to match the supply of vaccine with the anticipated demand. But they are also constrained by the amount that they can order from overseas. So they decided to order 500,000 doses per month.

There is now a dynamic interaction between three populations and the stock vaccine. The Unvaccinated Population generates a demand for a 1st Jab. Not all of the Unvaccinated Population will want to get vaccinated and some may wait to get vaccinated.

The unvaccinated population declines over time, while the population with two jabs increases. The population with one jab increases but at a declining rate over time. This is because people are just passing through this population on their way to the population with two jabs. The numbers are smaller over time because the unvaccinated population is declining.

After two years there is still a residual unvaccinated population.

The government priority was for first jabs. This meant there was no waiting for the first jab, but it took fully two years before the second jab was delivered to the total population.

The full model generated this data is very simple. The next stage will be to model the impact of an outbreak of the virus and a lockdown.