Typhoid Vaccine

Ira Shah
Consultant Pediatrician, B J Wadia Hospital for Children, Mumbai, India
First Created: 01/10/2001  Last Updated: 12/27/2023


Protection against enteric fever might be best achieved by a vaccine that stimulates IgG antibodies to "Vi" capsular polysaccharide in serum, IgG antibodies to "O" antigen in serum, and cell-mediated immune response.

Vi antigen vaccine

It contains the Vi polysaccharide antigen of S. Typhi. As Vi polysaccharide is the most important virulent factor, the antibodies against Vi antigen are protective against typhoid fever. It is a subunit-inactivated vaccine. It is freely available for use. Vi antigen vaccine is given in the dose of 0.5 ml intramuscularly either on the anterolateral aspect of the thigh or in the deltoid muscle. It is given as a single dose. It is given in children above 2 years of age.

Oral ty21a vaccine

This is no longer available. This is an oral live vaccine. It contains the ty21a strain of S. Typhi, which is a mutant strain lacking the UDP galactose epimerase enzyme. It induces local gut immunity without any systemic immunity. Live attenuated vaccine (Ty21a) is not able to elicit anti-Vi antibodies maybe because Vi expression is highly regulated. Also, unexpected symptoms like dizziness and pruritis, fatigue, and myalgia and occasional cases of reactive arthritis have also been reported with this vaccine. Oral ty21a vaccine is a course of 3 capsules given orally on alternate days. The capsules should be swallowed intact & not opened or chewed. In most, the pack contains 4 capsules and such 4 capsules are given on alternate days.

Since both these vaccines do not induce cell-mediated immunity, the protective efficacy lasts for 2-3 years in most of the vaccines, and booster doses are required every 2-3 years.

Vi-polysaccharide conjugate typhoid vaccine (TCV): It is a Vi-capsular polysaccharide conjugate typhoid vaccine conjugated with tetanus toxoid. The dose of Vi polysaccharide is 25 µg/0.5 mL. The vaccine has been licensed by the Drug Controller General of India (DCGI) in August 2013 for clinical use in India. This vaccine has been approved for use in children below 1 year of age. Though seroconversion rates of 98.05% have been reported with this vaccine, the antibody titers fall significantly after 18 months suggesting that a booster dose may be required. However, when the booster dose should be given can only be established on long term follow up. The Indian Academy of Pediatrics recommends that the TCV can be given below one year of age, preferably between 9-12 months (minimum age 6 months). Since the incompatibility data with the measles vaccine is not available, it would be prudent to maintain an interval of at least 4 weeks with the former.

Typhoid Vaccine Typhoid Vaccine https://www.pediatriconcall.com/show_article/default.aspx?main_cat=vaccinology&sub_cat=typhoid-vaccine&url=typhoid-vaccine-introduction 2023-12-27
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