Controlling endemic cholera with oral vaccines.
BACKGROUND
Although advances in rehydration therapy have made cholera a treatable disease with low case-fatality in settings with appropriate medical care, cholera continues to impose considerable mortality in the world's most impoverished populations. Internationally licensed, killed whole-cell based oral cholera vaccines (OCVs) have been available for over a decade, but have not been used for the control of cholera. Recently, these vaccines were shown to confer significant levels of herd protection, suggesting that the protective potential of these vaccines has been underestimated and that these vaccines may be highly effective in cholera control when deployed in mass immunization programs. We used a large-scale stochastic simulation model to investigate the possibility of controlling endemic cholera with OCVs.


RESULTS
We construct a large-scale, stochastic cholera transmission model of Matlab, Bangladesh. We find that cholera transmission could be controlled in endemic areas with 50% coverage with OCVs. At this level of coverage, the model predicts that there would be an 89% (95% confidence interval [CI] 72%-98%) reduction in cholera cases among the unvaccinated, and a 93% (95% CI 82%-99%) reduction overall in the entire population. Even a more modest coverage of 30% would result in a 76% (95% CI 44%-95%) reduction in cholera incidence for the population area covered. For populations that have less natural immunity than the population of Matlab, 70% coverage would probably be necessary for cholera control, i.e., an annual incidence rate of < or = 1 case per 1,000 people in the population.


CONCLUSIONS
Endemic cholera could be reduced to an annual incidence rate of < or = 1 case per 1,000 people in endemic areas with biennial vaccination with OCVs if coverage could reach 50%-70% depending on the level of prior immunity in the population. These vaccination efforts could be targeted with careful use of ecological data.
Longini
Ira M
IM
Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America. longini@scharp.org
Nizam
Azhar
A
Ali
Mohammad
M
Yunus
Mohammad
M
Shenvi
Neeta
N
Clemens
John D
JD
D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D001459:Bangladesh; D002648:Child; D002675:Child, Preschool; D002771:Cholera / Q000517:prevention & control*; D022121:Cholera Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D002986:Clinical Trials as Topic; D004196:Disease Outbreaks / Q000517:prevention & control; D006801:Humans; D007223:Infant; D015233:Models, Statistical; D008962:Models, Theoretical; D013269:Stochastic Processes; D014612:Vaccines
D022121:Cholera Vaccines; D014612:Vaccines