New Low-Cost Vaccine Offers Better Protection Against Cholera

The vaccine was found to offer elicit high levels of immunity in children, for whom the risk of endemic cholera is highest, as well as in adults. These responses were comparable to those elicited by a Swedish-made vaccine that has already been licensed for use in several European countries.

Work began in Viet Nam during the mid-1980s on the production of a killed oral cholera whole-cell vaccine that could be used in the country's public health programmes. The vaccine was later modified so that it could also counter a new form of epidemic cholera that emerged in the 1990s.

The two trials reported in the Bulletin were carried out in Hanoi and involved about 144 adults aged between 17 and 25 years and about 103 children aged 1-12 years. The trials were conducted by scientists from Viet Nam, Sweden, the United States, the Republic of Korea, the International Vaccine Institute in South Korea and the World Health Organization in Switzerland.

All the participants were given two doses of either the locally-produced vaccine, its Swedish counterpart, or a placebo, with the doses separated by an interval of two weeks. The trial in children began only after the trial in adults showed no important side-effects.

In both studies, the participants were observed for 30 minutes after each dose and were visited daily for three consecutive days to ascertain symptoms. Interviews were also conducted two weeks after each dose in order to obtain information about any intervening illnesses requiring medical care. Blood samples were taken for laboratory analysis.

The researchers found that the Vietnamese vaccine was associated with no side-effects and caused a better immune response in children than in adults, for reasons that were not clear. "The safety and immunogenicity of the vaccine, especially its ability to elicit robust responses, are encouraging, particularly because of its low cost of production (ca. US$ 0.20 per dose) in Viet Nam," the scientists say in the journal. They add that further studies are needed in order to evaluate the clinical protection it confers.