Seroprevalence of anti Vi antibodies and immunogenicity of Typhim Vi vaccine in children

This prospective study was carried out on 250 children between 6 months to 5 years of age to determine seroprevalence of anti Vi antibodies and to measure seroresponse and percent seroconversion to TyphimVi polysaccharide vaccine in children 2 - 5 years of age. Fifty children each were enrolled between 6 to 12 months of age ( Group A), between 1 - 2 years of age( Group B), between 2 - 3 years of age ( Group C), between 3 - 4 years of age ( Group D) and between 4 - 5 years of age ( Group E). Anti- Vi antibody baseline titres were determined in all children. Children in Groups C to E were vaccinated with Typhim Vi vaccine. Baseline and postvaccination antibody titres were determined by ELISA. Test sera which had antibody levels > 1 mu g/ ml were scored as seropositive. Of 250 children, 3 had base line anti- Vi antibodies > 1 mu/ ml. Following immunization overall seroconversion rate was 77.5% with 65.3%, 78.2% and 88% children showing seroconversion in Groups C, D and E respectively. Seroconversion was significantly more in Group E children compared to Group C ( p = 0.0148). There were no significant adverse reactions following vaccination. The study highlights very low prevalence of baseline anti Vi antibodies in children between 6 months and less than 5 years of age and shows high immunogenicity and safety of Typhim Vi polysaccharide vaccine in children 2 - 5 years of age.