Cholera vaccine: developmental strategies and problems.

Over a hundred years have elapsed since Vibrio cholerae, the etiological agent for the disease cholera, was discovered by Robert Koch. Ever since then serious efforts have been made to develop prophylactic measures to combat the disease without much success. Seven pandemics have so far been reported and cholera still remains a public health problem in developing countries. Several strategies have been adopted to develop vaccines against the disease and many of these vaccines have undergone field trials. During the last two decades, an enormous amount of information has accumulated regarding the organism V. cholerae, its virulence factors, including cholera toxin, and the molecular basis of its pathogenicity. In recent years, with the advent of recombinant DNA technology and major breakthroughs in molecular biology and immunology, a new dimension has been given to the design of vaccine strains. The second generation live oral vaccines will perhaps soon replace the long-used first generation parenterally administered killed whole cell vaccines which offered protection for not more than three months. All the recombinant vaccines tested so far produced adverse reactions in volunteers, although they provided varying degrees of protection upto about one year of surveillance. Parallel to the trials of live oral vaccines, combination vaccines comprising killed whole cells and purified B subunit of cholera toxin was also tried. These vaccines had minimal side-effects but the efficacy was not upto expectations. From the failure of each vaccine strain, new information had emerged and improved strategies were adopted.(ABSTRACT TRUNCATED AT 250 WORDS)