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While oral cholera vaccines have been available to protect travelers formore than a decade, they have not been used for widespread control of thedisease in cholera-prone (endemic) regions in part because their protectivepotential has been underestimated. In fact, using a computer simulation modelbased on data from a large-scale cholera-vaccine trial involving 200,000people in Matlab, Bangladesh, Longini and colleagues suggest thatinternationally licensed, killed whole-cell cholera vaccines (OCVs) may behighly effective in controlling cholera when given via mass immunization.
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Longini and colleagues estimate that cholera cases could be reduced nearly90 percent among the unvaccinated if just 50 percent of the populationreceived an oral vaccination biannually. Vaccinating just 30 percent of thepopulation every two years would achieve an overall cholera reduction rate of76 percent. In populations with less experience with cholera than Matlab, atleast 70 percent of the population would need to be vaccinated to control thedisease.
"This is the first scientific work that shows how we could control choleraon a global level," said Longini, also a professor of biostatistics at theUniversity of Washington School of Public Health and Community Medicine. "Onceyou get up to about 50 percent of the population vaccinated, you can drive theepidemic into practically nothing."
Endemic cholera is a bacterial infection of the small intestine thatcauses acute, watery diarrhea. If untreated, it can lead to potentially fataldehydration. Although advances in rehydration therapy have made cholera atreatable disease in areas with sufficient medical care, it remains a fatalcondition among the world's most impoverished populations. The disease iscaused by ingesting food or water contaminated with a comma-shaped bacteriumcalled Vibrio cholerae.
Co-authors on the paper included researchers from Emory University inAtlanta; the International Vaccine Institute in Seoul, Korea; and theInternational Centre for Diarrhoeal Disease Research in Bangladesh.
"These important findings stem from the recent recognition that oralvaccines against cholera confer herd protection -- protection of nonvaccinatedneighbors of vaccinated persons," said John Clemens, M.D., director-general ofthe International Vaccine Institute and paper co-author. "I believe this studywill have an impact on the public-health community's approach to controllingcholera," he said.
The research was supported by the Diseases of the Most Impoverished (DOMI)Program of the Bill & Melinda Gates Foundation, a grant from the NationalInstitute of General Medical Sciences Models of Infectious Disease Agent Study(MIDAS), and the U.S. National Institute of Allergy and Infectious Diseases.
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