There are a few diseases that are making a comeback, despite the fact that vaccines exist for them. Polio is an especially dire example.
There are many reasons for this, some of which are:
1) In disease-free areas, these diseases are unknown and thus have no power to terrify.
2) In some remote areas, it is difficult to supply the vaccine.
However, these two issues can be easily solved with the proposal below.
Modify a variety of snake so that it injects a helpful vaccine instead of a deadly neurotoxin.
These snakes could be airdropped over regions that were experiencing disease epidemics, where they would gracefully glide to the ground and get to work vaccinating the population.
The spitting cobra is a promising candidate for modification; it could supply the vaccine by spitting it into the eyes, rather than requiring a painful fang-ing.
PROS: Eradicates diseases. Puts unemployed snakes to work. Generates good will in foreign countries that are appreciative of the “snakeccination” effort.
CONS: None! You should go and lobby for funding for this idea right now.