1) The document discusses how infectious disease agents can be conceptualized as having their own wardrobes from which they select outfits that allow them to infect and survive within human hosts. 2) Certain diseases like measles have very limited wardrobes, making vaccines against them very effective, while diseases like influenza and malaria can change their outfits more easily through mutation. 3) The author presents a mathematical model showing that influenza's wardrobe may be more limited than previously believed, opening possibilities for improved vaccine design that targets conserved elements of the virus.