There are currently three licensed cholera vaccines available in various countries around the world. These include the old killed, whole-cell parenteral vaccine, the B subunit/killed whole-cell oral vaccine (BS/WCV),83,84 and live oral V cholerae O1 strain CVD 103-HgR.85,86 The BS/WCV is marketed under the trade name Dukoral (SBL, Stockholm, Sweden), whereas CVD 103-HgR is marketed as Orochol or Mutacol (Berna Biotech, Berne, Switzerland). Neither the nonliving nor the live oral cholera vaccine is presently licensed in the United States. Since the old killed, whole-cell vaccine is reactogenic and confers only partial, short-term protection, there has been little enthusiasm on the part of public health authorities to recommend its widespread use. The two new oral vaccines have distinct advantages over the old parenteral vaccine. They are easy to administer and are more potent in stimulating local intestinal immune responses. These vaccines protect against cholera caused by V cholerae serogroup O1 but not O139.
An advantage of the BS/WCV is its complete safety, even in immunocompromised subjects. A drawback to the BS/ WCV is the need for two to three doses to confer protection. The nonliving vaccine elicits only modest serum vibriocidal responses but strong antitoxin responses. If time and circumstances allow pre-emptive immunization, the BS/WCV can be successfully delivered despite the need for two spaced doses.87 Two randomized, controlled field trials assessed the efficacy of a two-dose regimen of the commercial formulation of the BS/WCV Two doses of BS/WCV conferred 86% protection upon young adult Peruvian military personnel over approximately 5 months of follow-up.83 A two-dose regimen did not confer significant protection upon Peruvian civilians (children and adults) during a year of follow-up.84 However, administration of a third dose conferred greater than 60% protection during a second year of follow-up.84
The safety and immunogenicity of single-dose live oral cholera vaccine strain CVD 103-HgR have been established in randomized, placebo-controlled, double-blind field trials in many developing and industrialized countries that have included thousands of young and elderly adults, children, and infants as young as 3 months of age.85,88-93 The live vaccine stimulates stronger serum vibriocidal responses than the nonliving vaccine but lesser antitoxic responses. Multiple small clinical trials demonstrated that a single oral dose of CVD 103-HgR confers greater than 90% protection against moderate or severe cholera caused by V cholerae O1 of either biotype or serotype85,86,94; the protective effect is evident as soon as 8 days after administration of vaccine.94 A single-dose regimen of CVD 103-HgR did not confer long-term protection against El Tor cholera in an endemic area.95 However, when used by the WHO in control of an epidemic of cholera in Micronesia (a situation where time and logistical constraints made it untenable to administer other than a single-dose vaccine), the single-dose live cholera vaccine exhibited 79% efficacy under field conditions.96
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