Cholera is one of the biggest killers of people. One of the Horseman of the Apocalypse (pestilence). It causes extreme diarrhea which can cause death from dehydration. It is spread through drinking water contaminated with human waste. Vaccines are now being tested in real non-lab situations. Vaccine numbers had been built up and are being used to immunize where outbreaks are occurring (the vaccines seem to more rapidly increase immunity than was initially expected) and being contemplated for use in more prophylactic situations.