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A cheap cholera vaccine is getting closer to international distribution after proving safe and effective in a large clinical trial.

The results, published today (9 October) in The Lancet, build on last year's encouraging results of a pilot trial of the vaccine (see Cheaper cholera vaccine passes pilot trial).

About sixty-seven thousand people aged one year or older living in cholera-prone Kolkata, India, completed the trial, receiving two doses of either vaccine or a placebo.

After two years, the vaccine had reduced cholera cases by around two-thirds in vaccinated people, was equally effective in all age groups and had no serious side effects.

Oral vaccines for cholera, which is caused by Vibrio cholerae bacteria, are available but often too expensive for endemic countries' public health programmes.

The vaccine is based on an earlier version manufactured and used in Vietnam. But Vietnam's drug regulatory authority is not approved by the WHO, and the vaccine did not meet WHO standards because the manufacturing process did not always remove cholera toxin from the vaccine.

Vietnamese manufacturer ViBiotech worked with the International Vaccine Institute to reformulate the vaccine and production has now moved to India where the regulatory authority is approved.

The authors write that because the vaccine is produced to WHO standards, the results may be sufficient to merit using the vaccine in public health programmes now.

But follow-up studies to confirm how long protection lasts and whether it can provide 'herd immunity' — protection of the unvaccinated by immunising most of the population — could make the vaccine more beneficial in the long term, they write.

Saranya Sridhar of the School of Public Health at the US-based University of California, Berkeley, agrees, writing in an accompanying comment: "Today's encouraging results must be tempered by cautious optimism as results from longer follow-up for evidence of lasting protection must be reviewed before this current vaccine is recommended as an alternative to the expensive [vaccine]".

Sridhar says that the vaccine must be directly compared with the WHO's recommended vaccine but that it "might be the first major step in the deployment of a cholera vaccine for mass immunisation in cholera-endemic areas".

The most notable feature of the vaccine, Sridhar writes, is its development via a public-private partnership. "This success story ought to be an example for other vaccine initiatives, especially against malaria and HIV, to similarly engage industry and academia towards solving an urgent public health need."

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