The project for "Introduction of Cholera Vaccine in Bangladesh" (ICVB) will examine the effectiveness of intervention with an oral cholera vaccine in reducing incidence of cholera in urban Dhaka, and the effectiveness of a handwashing and home water treatment behaviour change intervention in reducing diarrhea due to cholera. The proposal involves evaluation of a 2-dose regimen of an oral killed whole cell (WC) vaccine and a handwashing and home water treatment behavior change program promoting improved hygiene and home drinking water treatment in reducing dehydrating diarrhea in a low income area of Dhaka, Bangladesh. The study population will include 90 clusters (neighborhoods) in an area of high cholera incidence in Mirpur with a total study population of 240,000. Thirty clusters (approximately 80,000 people) will receive cholera vaccine alone, 30 clusters will receive both cholera vaccine and behavior change and 30 neighborhoods will continue their standard habits and practices. Surveillance for cholera and diarrhea will be carried out in all the three areas during the whole project period. Following the GIS mapping and census of the target populations, the cholera vaccine will be offered to all males and non-pregnant females aged one year and above in the vaccination areas, and an aggressive hygiene and safe water promotion program will be implemented in the 30 behavior change communication clusters. Passive surveillance for cholera will be undertaken using the two ICDDR,B diarrhea treatment facilities as well as 10 other health facilities that serve the study areas. Vaccine and other public health coverage and costs effectiveness as well cost-benefit will be measured, followed by surveillance and identical follow-up studies. The hygiene and safe water behavior change program will also be continued for 4 years. The impact of interventions will be assessed by following vaccination by directly comparing the incidence of cholera and diarrhea in the intervention communities to the incidence in the standard habits and practices communities.