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Cholera vaccines are vaccines that are effective in preventing cholera. They are about 85% effective during the first six months and 50–60% effective during the first year. The effectiveness decreases to less than 50% after two years. When a significant portion of the population is immunized benefits from herd immunity may occur among those not immunized. The World Health Organization recommends their use in combination with other measures among those at high risk. Two doses or three doses of the oral form are typically recommended. An injectable form is available in some, but not all, areas of the world.
Both of the available types of oral vaccine are generally safe. Mild abdominal pain or diarrhea may occur. They are safe in pregnancy and in those with poor immune function. They are licensed for use in more than 60 countries. It use in countries where the disease is common appears to be cost effective.
The first vaccines used against cholera were developed in the late 1800s. They were the first widely used vaccine that was made in a laboratory. Oral vaccines were first introduced in the 1990s. It is on the World Health Organization's List of Essential Medicines, the most important medication needed in a basic health system. The cost to immunize against cholera is between 0.1 and 4.0 USD.
Oral cholera vaccines are increasingly used as an additional tool to control cholera outbreaks in combination with the traditional interventions to improve safe 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. 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.
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.
Oral vaccines provide protection in 52% of cases the first year following vaccination and in 62% of cases the second year. 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.
Although rarely in use, the injected cholera vaccines are effective for people living where cholera is common. They offer some degree 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.
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