Anchilles fever was a highly contagious and virulent disease, capable of causing deaths numbering in the millions. The vaccine for the fever was extremely rare, and not able to be readily synthesized.
In 2364, the planet Styris IV suffered from a vicious outbreak of the disease. The only nearby source for the vaccine was Ligon II, which, after a brief negotiation, gave the USS Enterprise-D the supplies needed to cure the outbreak. (TNG: "Code of Honor")