A massive cholera vaccination campaign began on Monday to protect nearly one million Rohingyas and their host communities living in and around the refugee camps in Bangladesh to prevent any potential outbreak during the ongoing monsoon season. Earlier 900000 doses of oral cholera vaccine were administered to the vulnerable population in two phases in October - November last year. Considering the water and sanitation conditions in the overcrowded camps and the increased risk of disease outbreaks in the monsoon season the health sector is taking all possible measures to prevent cholera and other water and vector borne diseases said Dr.