Development of oral inactivated vaccines againstVibrio choleraeis associated with nonindustrial centres worldwide, including the International Centre for Diarrhoeal Disease Research (Bangladesh), University of Göteborg (Sweden), Mahidol University (Thailand), University of Maryland (USA), National Institutes of Health (USA) and the Walter Reed Army Institute of Research (USA).Researchers at the Mahidol University in Thailand have conducted clinical trials investigating the immunogenicity of their oral inactivated cholera vaccine.Researchers at the National Institute of Hygiene and Epidemiology in Hanoi, in Vietnam and the National Institute of Child Health and Human Development in Bethesda, Maryland, USA, are also conducting phase III clinical trials in Vietnam using a killed whole-cell vaccine, based onV. cholerae01 El Tor biotype. The vaccine is said to be effective and inexpensive but confers protection only against the 01 serogroup of cholera. The researchers were seeking to modify the vaccine further by the addition of killed 0139 cholera strain to the existing formulation. It appears that the government of Vietnam has now modified its whole-cell vaccine by adding a killedV. cholerae0139 strain to the existing vaccine formulation and phase II trials with the bivalent vaccine were to begin in 1997.