Beating the cholera bug

By Biplab Das
Published: Friday 15 August 2008

Vaccine from Vietnam found effective in a trial in Kolkata

A new reformulated oral cholera vaccine (ocv), earlier tested and found effective in Vietnam, was found to be safe in a cholera endemic region in Kolkata.After further studies, if the vaccine is found safe and protective, it could pave the way for its wide use in the control of cholera worldwide.

So far, two oral vaccines have international licences but they have limitations. The first, made from a genetically modified bit of cholera toxin, cannot be given to children under two. The other vaccine, called the travellers' vaccine, failed to show convincing protection against field trials in Indonesia. This is made from live attenuated bacterium. These limitations led researchers to devise the ocv that does not contain any part of the cholera toxin. It is made from killed bacterium and contains lipopolysaccharide (lps), a major component of the cell wall of predominant circulating strains of the cholera bug.

Since 1997, more than nine million doses of this bivalent vaccine have been administered in Vietnam and no serious adverse events have been associated with this vaccine. For the Indian study, Korea-based International Vaccine Institute and Shantha Biotechnic in Hyderabad reformulated the vaccine.

The trial in Kolkata was conducted among 101 adults (18-40 years old) and 100 children. The vaccine or placebo was given in two doses separated by a two-week interval and administered orally. Blood samples were obtained prior to the first dose and 14 days after the second dose and analyzed.

The vaccine increased the antibodies, cells that could destroy the cholera bug. The adults showed a 4.5-fold rise in antibody levels and children a 12.3-fold increase. The study is published in PloS One (Vol 3, No 6). "The advantage of this vaccine is that it does not contain toxins that could cause the disease," said Dipika Sur, co-researcher of the study. "The existing vaccines have same efficacy but most of them are much more expensive. "We estimate each dose of the present vaccine to cost about us $1 (Rs 41)," Sur adds. In Vietnam, the vaccine is produced at about us $0.40 per dose.

According to Salil Kumar Bhattacharya, head of the department of community medicine at the National Medical College Hospital, Kolkata, "The new vaccine appears safe as it contains lps of various heat-killed cholera strains. But further research needs to be done. Stress should also be given on washing hands before eating and after defecation and access to oral rehydration solution. This too would reduce cholera induced morbidity to a great extent." The next step is a large-scale community-based study in Kolkata, currently underway.

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