By Ryan Heneghan
In today’s increasingly connected world, the reality of infectious epidemics is a permanent fixture in the background of our modern consciousness. From movies like Contagion to the 28 Days Later franchise, the notion of a destructive, unseen infection spreading through a city or country is capturing more of the general public’s imagination. The problem of controlling and stopping the spread of an epidemic is a very real one for public health professionals and when coupled with the reality of a limited quantity of vaccine, the question quickly becomes, “How can we stop an epidemic from spreading with the least vaccine?”. An answer to this question can be found using mathematics.
Mathematicians have designed models of populations that reflect the fact that different types of individuals will react to and spread an infection in different ways. These models can also be built in a way that realistically includes the interactions between an individual’s families and friends in the greater population. The model I looked at consisted of a population of adults and children, where children not only spread the infection more than the adults, they also had a higher risk of dying as a result of becoming infected. I examined and compared the effects of three different vaccination strategies. The first involved vaccinating children first, the second was where vaccinations would be given randomly irrespective of whether an individual was an adult or a child and the third strategy involved vaccinating adults first. I focussed on comparing the proportion of the population who died under these three strategies. The figure below shows the results.
The plot shows that vaccinating children first would be the way to go in this scenario, as it takes almost double the vaccine if we start with adults to prevent the epidemic from taking off and around one third less than the random allocation strategy.
Mathematical modelling matters when it comes to epidemics. It can even save lives by helping to find the best way of using often limited resources in the face of a potentially deadly epidemic.
Ryan Heneghan was one of the recipients of a 2013/14 AMSI Vacation Research Scholarship.