title: A Study on Longevity of Immune Response after Vaccination with Salmonella Typhi Vi Conjugate Vaccine (Pedatyph™) in Children.
abstract: OBJECTIVE
  Owing to the limitations of the conventional polysaccharide vaccines, global efforts have been made to develop conjugated polysaccharide vaccines for typhoid. Duration of immune response induced by these vaccines is critical to define the efficacy and frequency of required booster dose. This study was done to determine the duration of immune response following vaccination with Salmonella Typhi Vi conjugate vaccine (Pedatyph™) in children and to assess the booster effect of second dose of conjugate typhoid vaccine.
  
  
  METHODS
  Forty children were recalled from a cohort of 400 children, who received one dose or two doses of PedaTyph™, 30 months after vaccination. Ten non-vaccinated children were also recalled. Their serum samples were assessed by ELISA for anti Vi antibody.
  
  
  RESULTS
  Significantly high titers of anti-Vi polysaccharide IgG antibodies were present in vaccinated children even after 30 months of vaccination as compared to non-vaccinated children. Geometric mean titers (GMT) with 95% confidence intervals were 14 (4.8-29.8), 17 (7.4-33) and 6.4 (0.8-12) μg/ml for single dose, two doses and control group respectively. The children in two doses group had higher antibody titers as compared to single dose group. However, the difference was not significant.
  
  
  CONCLUSIONS
  PedaTyph™ was found to induce long term immune response as evidenced by presence of significant anti-Vi polysaccharide antibodies after 30 months of vaccination. No significant advantage of two doses regimen over one dose was found. Hence one dose vaccination with PedaTyph™ is suggested.
authors.affiliation: Associate Professor, Department of Paediatrics, SRM MCH& RC , Chennai, India .
authors.forename: Balaji
authors.initials: B
authors.lastname: Chinnasami
authors.affiliation: Assistant Professor, Department of Physiology, SRM MCH& RC , Chennai, India .
authors.forename: Kanimozhi
authors.initials: K
authors.lastname: Sadasivam
authors.affiliation: Researcher, Department of Immunology and Molecular Biology, AU-KBC Research Centre, MIT Campus of Anna University , Chrompet, Chennai, India .
authors.forename: Aravindhan
authors.initials: A
authors.lastname: Vivekanandhan
authors.affiliation: Former, Professor & HOD, Department of Paediatrics, SRM MCH& RC , Chennai, India .
authors.forename: Prema
authors.initials: P
authors.lastname: Arunachalam
authors.affiliation: Professor & HOD, Department of Paediatrics, SRM MCH& RC , Chennai, India .
authors.forename: Sekar
authors.initials: S
authors.lastname: Pasupathy
keywords: Conjugate typhoid vaccine; Salmonella; Salmonella Typhi; Typhoid, Vaccine