Its not really a new preventative treatment at all. This idea has been implemented for many other things. Think allergy shots that people get over the course of years. Allergies are an immune response to something that normally doesn't elicit an immune response. By taking small doses and increasing the dose each time your are conditioning your body to not respond to these things. Its obviously a lot more complicated than that with the involvement of B cell subsets, T cell subsets, Macrophages, Mast Cells, etc... essentially all immune cells. Its actually surprising it hasn't happened earlier for peanut allergies. There also two strong camps debating why people have more allergies, peanuts included. There are those that claim the hygiene hypothesis, there are others that claim its much more complicated than that.