ARE student François Castonguay presented his research on vaccine preventable diseases. Vaccine hesitancy—the delay in acceptance or refusal of vaccines despite availability of vaccination services—is one of the top threats to global health and is believed to be responsible for the resurgence of eliminated diseases such as measles. François investigates vaccine hesitancy in two ways: (i) he estimates the effect of vaccine licensing on disease prevalence across states in the US and (ii) he estimates a county-level dynamic model of disease transmission for the state of California. François finds that the licensing of the measles, mumps, rubella (MMR) and polio vaccines had a heterogenous effect on disease prevalence across states. The results of the dynamic model suggest that for pertussis (whooping cough) the vast majority of counties in California have vaccination levels below the recommended threshold and that susceptibility of infection is highly heterogeneous across counties.