Mass Oral Cholera Vaccination in Zanzibar

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Brief Title

Mass Oral Cholera Vaccination in Zanzibar

Official Title

Mass Oral Cholera Vaccination in High-risk Populations in Zanzibar: Assessment of Effectiveness and Herd Protection

Brief Summary

      The purpose of this study is to conduct cholera vaccinations in high-risk populations in
      Zanzibar in order to estimate herd protection conferred by the vaccine,estimate effectiveness
      of the vaccine, and describe the interaction of vaccination and improved water supply on the
      burden of cholera and diarrhoeal diseases.

Detailed Description

      The seventh cholera pandemic began in Indonesia in 1961 and spread quickly to other Asian
      countries. In 1970, the etiologic agent, Vibrio cholerae O1 El Tor, invaded sub-Saharan
      Africa, whose residents had not experienced cholera for more than 100 years. Outbreaks
      rapidly occurred and the disease has become endemic in several parts of the continent. In
      2006, Africa reported 234,349 cholera cases to the WHO, accounting for 99% of the
      officially-notified global cholera (1). Between 1995 and 2005, 66% of cholera outbreak
      reports to ProMed came from sub-Saharan Africa (2). There is growing evidence of the large
      and increasing burden of cholera in Africa.

      One African country that is severely and repeatedly affected by cholera is Zanzibar. After
      the first case of cholera was confirmed in the country in January 1978, regular outbreaks
      have been reported (3). These outbreaks cause human suffering, are socially disruptive, and
      divert resources from other essential services. Cholera control in Zanzibar has focused
      mainly on case management, water chlorination campaigns, and dissemination of hygiene
      messages. The Ministry of Health and Social Welfare (MOHSW) is eager to identify new and
      effective tools, such as oral cholera vaccination, that could be implemented in Zanzibar.

      In 2002, the World Health Organization (WHO) recommended the potential use of oral cholera
      vaccines in endemic and epidemic situations, but it was deemed necessary to gain more
      experience through demonstration projects (4). Since then, mass oral cholera vaccinations
      have been conducted in Beira, Mozambique (5), in Darfour, Sudan, and in Aceh, Indonesia which
      demonstrated the feasibility and effectiveness of vaccination under actual public health
      conditions. The only oral cholera vaccine available in the market consists of killed
      whole-cell V. cholerae O1 with purified recombinant B-subunit of cholera toxin (WC/rBS)
      administered with a buffer solution as two doses, at least a week apart. The vaccine is
      internationally-licensed (including in Zanzibar) for use in individuals 2 years of age and
      older. This vaccine, and its predecessor (BS-WC) that contained chemically extracted rather
      than recombinant cholera toxin B subunit, have been shown to be safe and protective in
      several trials conducted in cholera-endemic settings in Asia and South America (6-9) and in a
      sub-Saharan African setting with a high prevalence of HIV (5).

      An incompletely answered question regarding this vaccine is its potential to confer herd
      protection (10). The level of herd immunity would determine the minimum vaccine coverage
      required to produce widespread protection against cholera in a community. A recent study
      comparing cholera rates in sites in Asia and Africa has shown that the burden of cholera is
      greatest in young children (11); herd immunity would provide protection for children too
      young to receive the vaccine, as well as other unvaccinated members of the community.
      Although recent re-analysis of data from the large placebo-controlled field trials of the
      oral cholera vaccine in Bangladesh in the 1980s showed substantial herd protection from
      vaccination (12,13), there may be limitations to the applicability of these findings to other
      cholera endemic settings with different living conditions (14). Mathematical modelling of the
      same Bangladesh data found that cholera transmission could be controlled in endemic areas
      with 50% vaccine coverage. At this level of coverage, the model predicted that there would be
      an 89% reduction in cholera cases among the unvaccinated, and a 93% reduction overall in the
      entire population. A more modest coverage of 30% would result in a 76% reduction in cholera
      incidence for the population area covered (15). If confirmed in actual field studies, these
      mathematical predictions have major vaccine cost-effectiveness implications.

      We propose to carry out mass oral cholera vaccinations in populations at high risk for
      cholera in Zanzibar followed by an assessment of direct and indirect protection. The WHO was
      awarded a grant by the Bill and Melinda Gates Foundation entitled: "Pre-emptive use of a
      cholera vaccine in vulnerable populations at risk", under which this proposal will be funded.
      The 6 million US$ grant aims to address issues regarding the potential utilization and
      mechanism of pre-emptive delivery of the vaccine to prevent outbreaks in endemic regions. An
      important component is the potential creation of a "revolving" stock of vaccine and the
      financial sustainability of maintaining such a stockpile.

      The lessons learned from this project will be crucial for informed decisions about the
      potential wider use of cholera vaccination in Zanzibar and other cholera-endemic sub-Saharan
      African countries. The lessons learned from the effectiveness study will form part of the
      evidence for the possible establishment of a sustainable vaccine stockpile. The project would
      provide essential information on the vaccine coverage required to control cholera in endemic
      areas and additional data on vaccine effectiveness in a different setting in Africa.

Study Type


Primary Outcome

Receipt of 2 complete or nearly complete swallowed doses of oral cholera vaccine

Secondary Outcome

 Acute, non-bloody diarrhoea severe enough to seek care at the Primary Health Care Units




rBS-WC vaccine

Study Arms / Comparison Groups

Description:  This is a single arm study. All consenting, eligible participants will receive the oral cholera vaccine.


* Includes publications given by the data provider as well as publications identified by National Clinical Trials Identifier (NCT ID) in Medline.

Recruitment Information

Recruitment Status


Estimated Enrollment


Start Date

January 2009

Completion Date

December 2011

Primary Completion Date

February 2009

Eligibility Criteria

        Inclusion Criteria:

          -  Healthy residents of selected vaccination sites

          -  Aged 2 years and older

          -  non-pregnant

        Exclusion Criteria:

          -  Age less than 2 years

          -  Pregnant




2 Years - N/A

Accepts Healthy Volunteers

Accepts Healthy Volunteers


Ahmed Khatib, MD, , 

Location Countries


Location Countries


Administrative Informations



Organization ID

DK - 02

Responsible Party


Study Sponsor

International Vaccine Institute


 Ministry of Health and Social Welfare, Zanzibar

Study Sponsor

Ahmed Khatib, MD, Principal Investigator, Ministry of Health and Social Welfare, Zanzibar

Verification Date

March 2012