Three diseases, diarrhea, malaria, and pneumonia, account for 75% of all child deaths in Africa. Thus, it is possible that investments to prevent any one of these diseases depends on the prevalence of the other two; for example, there is little incentive for a family to invest in malaria prevention if their child will die from diarrhea regardless. Using this notion, I develop a model to explain the apparent inconsistent behavior of families in Africa spending relatively large amounts on medical treatment, but investing little in disease prevention and exhibiting substantial price sensitivity for prevention. In my model, investments in prevention for two diseases are complements, and disease prevention and medical treatment are substitutes. Thus, factors causing low levels of diarrhea prevention will cause low levels of malaria prevention, high price sensitive for malaria prevention, and high levels of treatment spending. I empirically test these predictions in the context of malaria and diarrhea in Africa using child vitamin A supplementation programs as an exogenous increase in prevention of diarrhea mortality. The results of this analysis support the predictions of the model, demonstrating that vitamin A supplementation leads to increased investment in malaria prevention, decreased price sensitivity for malaria prevention, and decreased treatment spending