Photo by Dean Forbes
Endemic cholera, a potentially fatal disease found in the world's most impoverished countries, could be effectively controlled by orally vaccinating half of the affected populations once every two years for only pennies per dose. This finding by an international team of researchers led by Dr. Ira Longini, a biostatistician with the Center's Vaccine and Infectious Disease Institute, was described in the Nov. 27 online edition of PLoS Medicine.
While oral cholera vaccines have been available to protect travelers for more than a decade, there has been no use of the vaccines for widespread control of the disease in cholera-prone (endemic) regions in part because of their underestimated protective potential. In fact, using a computer simulation model based on data from a large-scale cholera-vaccine trial involving 200,000 people in Matlab, Bangladesh, Longini and colleagues suggest that internationally licensed, killed whole-cell cholera vaccines (OCVs) may be highly effective in controlling cholera when given via mass immunization.
Ending an epidemic
Longini and colleagues estimate that cholera cases could be reduced nearly 90 percent among the unvaccinated if just 50 percent of the population received an oral vaccination biannually. Vaccinating just 30 percent of the population every two years would achieve an overall cholera reduction rate of 76 percent. In populations with less experience with cholera than Matlab, at least 70 percent of the population would need to be vaccinated to control the disease.
"This is the first scientific work that shows how we could control cholera on a global level," said Longini, also a professor of biostatistics at the University of Washington School of Public Health and Community Medicine. "Once you get up to about 50 percent of the population vaccinated you can drive the epidemic into practically nothing."
Endemic cholera is a bacterial infection of the small intestine that causes acute, watery diarrhea. If untreated, it can lead to potentially fatal dehydration. Although advances in rehydration therapy have made cholera a treatable disease in areas with sufficient medical care, it remains a fatal condition among the world's most impoverished populations. Ingesting food or water contaminated with a comma-shaped bacterium called Vibrio cholerae causes the disease.
Co-authors on the paper included researchers from Emory University in Atlanta; the International Vaccine Institute in Seoul, Korea; and the International Centre for Diarrhoeal Disease Research in Bangladesh.
"These important findings stem from the recent recognition that oral vaccines against cholera confer herd protection — protection of non-vaccinated neighbors of vaccinated persons," said Dr. John Clemens, director-general of the International Vaccine Institute and paper co-author. "I believe this study will have an impact on the public-health community's approach to controlling cholera," he said.
The Diseases of the Most Impoverished (DOMI) Program of the Bill & Melinda Gates Foundation, a grant from the National Institute of General Medical Sciences Models of Infectious Disease Agent Study (MIDAS), and the U.S. National Institute of Allergy and Infectious Diseases supported the research.