Typhoid immunisation

Abstract

Since the desired improvement in the sanitation and nealth facilities is not likely in most areas of the third world in the near future, the necessity for typhoid vaccination cannot be easily disputed. The mechanisms of immune response in typhoid, especially with regard to the local gut factors are poorly understood. Parental vaccines have been in use for over 80 yr, but controlled field trials establishing their efficacy were conducted barely two decades back. Several studies in endemic areas under the auspices of the World Health Organisation established success in providing 51 to 94 percent protection with parenteral typhoid vaccine. The immunity, however, is not as complete as with some viral or toxoid vaccines, and can be overcome by a large infective dose of S. typhi. The acetone-inactivated vaccine is superior to other vaccines. Two sub-cutaneous doses of 0.5 ml each are as effective as intradermal doses of 0.1 ml each. The intradermal administration causes less local and systemic reactions. A mutant strain of Salmonella typhi Ty 21 a, lacking UDP galactose epimerase enzyme showed promise as a live oral vaccine in volunteer and field trials. More work, however, is needed to establish its efficacy and practical utility. This vaccine may possibly be the most effective vaccine ever prepared for typhoid fever. oral killed vaccine has been shown to have no beneficial effect in controlled trials. New modalities in developing vaccines such as using Vi capsular polysaccharide antigen and other mutants of S. typhi are being worked out.