stochastic model
What's it like being a research mathematician and figurehead of Europe's representative body for mathematics? Find out in our interview with Marta SanzSolé. 
Dengue fever does the opposite of what you might expect. Unlike for many diseases, if you've had this tropical virus and recovered, you might be worse off, as a second exposure to the dengue virus can be life threatening. So keeping track of the strains of the diseases is an important problem which can be solved with the help of a little randomness. 
Researchers have used mathematical modelling to understand the evolution of the influenza virus.
