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Cholera vaccine

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Cholera vaccine

Cholera vaccine is a vaccine used against cholera.[1] The first vaccines used against cholera were developed in the late nineteenth century. These injected whole cell vaccine became increasingly popular until they were replaced by oral vaccines starting in the 1980s. Both oral and injectable forms are about 50-60% effective in the first year.[2][3]

Effectiveness

Oral

Oral vaccines provide protection in 52% of cases the first year following vaccination and in 62% of cases the second year.[3] There are two variants of the oral vaccine currently in use: WC-rBS and BivWC. WC-rBS (marketed as "Dukoral") is a monovalent inactivated vaccine containing killed whole cells of V. cholerae O1 plus additional recombinant cholera toxin B subunit. BivWC (marketed as "Shanchol" and "mORCVAX") is a bivalent inactivated vaccine containing killed whole cells of V. cholerae O1 and V. cholerae O139. mORCVAX is only available in Vietnam.

Bacterial strains of both Inaba and Ogawa serotypes and of El Tor and Classical biotypes are included in the vaccine. Dukoral is taken orally with bicarbonate buffer, which protects the antigens from the gastric acid. The vaccine acts by inducing antibodies against both the bacterial components and CTB. The antibacterial intestinal antibodies prevent the bacteria from attaching to the intestinal wall thereby impeding colonisation of V. cholerae O1. The anti-toxin intestinal antibodies prevent the cholera toxin from binding to the intestinal mucosal surface thereby preventing the toxin-mediated diarrhoeal symptoms.[4]

Injectable

Although no longer in use, the injected cholera vaccines are effective for people living where cholera is endemic. They offer significant degrees of protection for up to two years after a single shot, and for three to four years with annual booster. They reduce the risk of death from cholera by 50% in the first year after vaccination.[2]

Use

Oral cholera vaccines are increasingly used as an additional tool to control cholera outbreaks in combination with the traditional interventions to improve water supply, sanitation, handwashing and other means to improve hygiene. Since licensure of Dukoral and Shanchol, over a million doses of these vaccines have been deployed in various mass oral cholera campaigns around the world.[5] In addition, Vietnam incorporates oral cholera vaccination in its public health programme and over 9 million doses have been administered through targeted mass vaccination or immunization of school-aged children in cholera endemic regions.

The cholera vaccine is largely used by backpackers and persons visiting locations where there is a high risk of cholera infection. However, since it does not provide 100% immunity from the disease, food hygiene precautions should also be taken into consideration when visiting an area where there is a high risk of becoming infected with cholera. Although the protection observed has been described as "moderate", herd immunity can multiply the effectiveness of vaccination. Dukoral has been licensed for children 2 years of age and older, Shanchol for children 1 year of age and older. The administration of the vaccine to adults confers additional indirect protection (herd immunity) to children.

The WHO recommends both preventive and reactive use of the vaccine, making the following key statements:[6] WHO recommends that current available cholera vaccines be used as complements to traditional control and preventive measures in areas where the disease is endemic and should be considered in areas at risk for outbreaks. Vaccination should not disrupt the provision of other high priority health interventions to control or prevent cholera outbreaks. Reactive vaccination might be considered in view of limiting the extent of large prolonged outbreaks, provided the local infrastructure allows it, and an in-depth analysis of past cholera data and identification of a defined target area have been performed.

The WHO has received funding to organise an OCV stockpile, which will supply oral cholera vaccine in areas of emergency need.

References

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