Cholera: Cheaper Oral Vaccine Is Effective Early in Outbreak

Laurie Barclay, MD

May 28, 2014

A less less-expensive oral vaccine was effective when used in a cholera outbreak in Guinea, supporting the addition of vaccination to outbreak response, according to a matched case-control study published in the May 29 issue of the New England Journal of Medicine.

"The use of vaccines to prevent and control cholera is currently under debate," write Francisco J. Luquero, MD, MPH, from Epicentre, Paris, France, and colleagues. "Shanchol [Shantha Biotec] is one of the two oral cholera vaccines [OCVs] prequalified by the World Health Organization; however, its effectiveness under field conditions and the protection it confers in the first months after administration remain unknown. The main objective of this study was to estimate the short-term effectiveness of two doses of Shanchol used as a part of the integrated response to a cholera outbreak in Africa."

The researchers used a rapid test to confirm and enroll 40 case patients with cholera between May 20 and October 19, 2012. They selected 160 sex- and age-matched control participants from neighbors of the patients. The researchers used bivariate and adjusted conditional logistic-regression models to compare the odds ratio of vaccination between case patients and control patients, which allowed calculation of vaccine effectiveness.

OCV Effective in Outbreak

Vaccination with 2 complete doses of oral vaccine was associated with significant protection against cholera (effectiveness, 86.6%; 95% confidence interval, 56.7% - 95.8%; P = .001), after adjustment for demographic, environmental, and socioeconomic factors.

In light of previous research, the findings of this study suggest that the protection offered by Shanchol may be higher in the first 6 months than in the subsequent 2 years after vaccination, the authors note.

"In this study, Shanchol was effective when used in response to a cholera outbreak in Guinea," the study authors write. "This study provides evidence supporting the addition of vaccination as part of the response to an outbreak. It also supports the ongoing efforts to establish a cholera vaccine stockpile for emergency use, which would enhance outbreak prevention and control strategies."

Limitations of this study include a failure to control for exposure to the vaccine in the population; a small sample, limiting the possibility of conducting analyses stratified by age; and the inability to confirm vaccination status for all participants. In addition, the study was underpowered to provide precise estimates of the protection offered by a single dose of vaccine, which could substantially simplify vaccination in outbreaks.

In an accompanying editorial, Jean William Pape, MD, and Vanessa Rouzier, MD, from Les Centres GHESKIO, Port-au-Prince, Haiti, note that the study findings support the World Health Organization's current strategy of using OCV.

"Since 2010, some major obstacles preventing the use of OCV have been overcome," the editorialists write. "Shanchol, the cheapest and easiest-to-administer vaccine, is being stockpiled. OCV has been used in 13 countries on three continents (Asia, Africa, and the North American Caribbean) and in three risk settings. The study by Luquero et al. provides further evidence in favor of using OCV in emerging outbreaks."

Médecins sans Frontières funded this study. The editorialists and study authors have disclosed no relevant financial relationships.

N Engl J Med. 2014;370:2111-2120.


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