Background: Cholera is a cause of acute watery diarrhoea which can cause dehydration and death if not adequately treated. It usually occurs in epidemics, and is associated with poverty and poor sanitation. Effective, cheap, and easy to administer vaccines could help prevent epidemics.

Objectives: To assess the effectiveness and safety of oral cholera vaccines in preventing cases of cholera and deaths from cholera.

Search methods: In October 2010, we searched the Cochrane Infectious Disease Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; the metaRegister of Controlled Trials (mRCT), and the WHO International Clinical Trials Registry Platform (ICTRP) for relevant published and ongoing trials.

Selection criteria: Randomized or quasi-randomized controlled trials of oral cholera vaccines in healthy adults and children.

Data collection and analysis: Each trial was assessed for eligibility and risk of bias by two authors working independently. Data was extracted by two independent reviewers and analysed using the Review Manager 5 software. Outcomes are reported as vaccine protective efficacy (VE) with 95% confidence intervals (CIs).

Main results: Seven large efficacy trials, four small artificial challenge studies, and 29 safety trials contributed data to this review.

Five variations of a killed whole cell vaccine have been evaluated in large scale efficacy trials (four trials, 249,935 participants). The overall vaccine efficacy during the first year was 52% (95% CI 35% to 65%), and during the second year was 62% (95% CI 51% to 62%). Protective efficacy was lower in children aged less than 5 years; 38% (95% CI 20% to 53%) compared to older children and adults; 66% (95% CI 57% to 73%).

One trial of a killed whole cell vaccine amongst military recruits demonstrated 86% protective efficacy (95% CI 37% to 97%) in a small epidemic occurring within 4 weeks of the 2-dose schedule (one trial, 1426 participants). Efficacy data is not available beyond two years for the currently available vaccine formulations, but based on data from older trials is unlikely to last beyond three years.

The safety data available on killed whole cell vaccines have not demonstrated any clinically significant increase in adverse events compared to placebo.

Only one live attenuated vaccine has reached Phase III clinical evaluation and was not effective (one trial, 67,508 participants). Two new candidate live attenuated vaccines have demonstrated clinical effectiveness in small artificial challenge studies, but are still in development.

Authors' conclusions: The currently available oral killed whole cell vaccines can prevent 50 to 60% of cholera episodes during the first two years after the primary vaccination schedule. The impact and cost-effectiveness of adopting oral cholera vaccines into the routine vaccination schedule of endemic countries will depend on the prevalence of cholera, the frequency of epidemics, and access to basic services providing rapid rehydration therapy.

/pdf/oral-vaccines-for-preventing-cholera-12e27lsaap.pdf

Oral vaccines for preventing cholera

In response to the epidemiological situation, live attenuated or killed vaccines against anthrax, brucellosis, cholera, glanders, plague and tularemia were developed and used for immunization of at-risk populations in the Former Soviet Union. Certain of these vaccines have been updated and currently they are used on a selective basis, mainly for high risk occupations, in the Russian Federation. Except for anthrax and cholera these vaccines currently are the only licensed products available for protection against the most dangerous bacterial pathogens. Development of improved formulations and new products is ongoing.

Russian vaccines against especially dangerous bacterial pathogens.

BACKGROUND Oral cholera vaccines (either killed whole cell or live recombinant vaccines) are newer alternatives to the parenteral vaccines which have been thought to confer only moderate and short-term immunity. OBJECTIVES The objective of this review was to assess the effect of cholera vaccines in preventing cases of cholera and preventing deaths. SEARCH STRATEGY We searched the Cochrane Infectious Diseases Group trials register, Medline, Embase and reference lists of articles. We handsearched the journal Vaccine, contacted researchers in the field and manufacturers. SELECTION CRITERIA Randomised and quasi-randomised studies comparing cholera vaccines (killed or live) with placebo, control vaccines or no intervention, or comparing types, doses or schedules of cholera vaccine. We included adults and children irrespective of immune status or special risk category. DATA COLLECTION AND ANALYSIS Data extraction and assessment of trial quality was done independently by two reviewers. MAIN RESULTS Thirty-two trials were included. Seventeen efficacy trials of relatively good quality, testing parenteral and oral killed whole cell vaccines and involving over 2. 6 million adults, children and infants were included. Nineteen safety trials have been conducted for both types of killed whole cell vaccines and for live vaccines and have involved 11,459 people. For all types of vaccines compared to placebo, the relative risk of contracting cholera at 12 months was 0.49, 95% confidence interval 0. 41 to 0.59 (random effects model). This translates to an efficacy of 51%, 95% confidence interval 41% to 59%. Both parenteral and oral administration were relatively efficacious, but significant protection extended into the third year for oral killed whole cell vaccines. Children under 5 were only protected for up to a year, while older children or adults were protected for up to three years. Parenteral killed whole cell vaccines were associated with increased systemic and local adverse effects compared to placebo. Oral killed whole cell vaccines or oral live vaccines were not. REVIEWER'S CONCLUSIONS Cholera killed whole cell vaccines appear to be relatively effective and safe. Live oral recombinant vaccines appear to be safe, but efficacy data are not available. Protection against cholera appears to persist for up to two years following a single dose of vaccine, and for three to four years with an annual booster.

Vaccines for preventing cholera

Development of Heterologous Expression System and Optimization of the Method of Cholera Toxin β-Subunit Production in E. coli

The reactogenic properties and immunological potency of modified cholera chemical vaccine (choleragen-toxoid + O-antigens Inaba and Ogawa) were tested in 278 volunteers aged 18 years and over in comparison with those of a commercial batch of monovalent cholera vaccine (choleragen-toxoid + O-antigen Inaba). The cholera vaccine, enriched with O-antigen Ogawa, was found to be safe; vaccination with this vaccine was not accompanied by the development of systemic and local reactions whose frequency and intensity met the requirements for the reactogenic properties of commercial cholera vaccine. The immunological potency of the bivalent vaccine with respect to strain Inaba was not inferior to that of the commercial vaccine; at the same time in persons immunized with the new preparation the titers of vibriocidal antibodies to strain of serovar Inaba were five-fold higher. The conclusion on the expediency of using cholera chemical vaccine enriched with O-antigen Ogawa was made.

The characteristics of the reactogenicity and immunological activity of a new cholera bivalent chemical vaccine based on the results of controlled trials

276 volunteers aged 19 years and over were placed under observation in the course of the trial of oral cholera vaccine in tablets, containing choleragen toxoid, O-antigens of serovars Inaba and Ogawa and a number of Vibrio cholerae exoenzymes, for safety, reactogenic properties and immunological effectiveness. The vaccine was found to produce no reactions in a dose of 1-4 tablets; the administration of 3 tablets (300,000 binding units of the toxoid and 10,000 units of O-antigens, serovars Inaba and Ogawa) was shown to induce the most intensive synthesis of both antitoxins and vibriocidal antibodies in the blood sera of volunteers, as well as IgA coproantibodies. The oral vaccine was found to have an advantage over parenteral vaccines due to the absence of reactogenic properties and the formation of local immunity: coproantibodies appeared in 80% and 9% of the vaccinees respectively.

The determination of the optimal inoculation dose of an oral cholera chemical bivalent vaccine in a controlled experiment

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The characteristics of the reactogenicity and immunological activity of a new cholera bivalent chemical vaccine based on the results of controlled trials

The determination of the optimal inoculation dose of an oral cholera chemical bivalent vaccine in a controlled experiment