Where was the first vaccine against cholera first tested in field settings?

Field testing of cholera vaccines has long been associated with South Asia, particularly Bangladesh and India, where cholera has been a recurring public-health problem. Researchers worked in settings where the disease was endemic so they could study real-world protection. Modern oral cholera vaccines are now used in outbreak response and in areas with ongoing risk. Cholera spreads through contaminated water and food, making sanitation as important as vaccination. Field experience in South Asia helped shape current vaccine strategies.