PediaNotes

Typhoid Vaccine

2 min read

Disease Burden And Rationale

  • Enteric fever caused by Salmonella Typhi heavily impacts low-income and middle-income nations.
  • Children under 15 years carry highest disease burden.
  • Rising extensively drug-resistant strains necessitate effective prevention.
  • Immunization reduces transmission, severe complications, and hospitalization.

Vi Capsular Polysaccharide Vaccine

Composition And Immunology

  • Comprises 25 µg purified Vi-polysaccharide.
  • Functions as T-cell independent antigen.
  • Fails to generate immunological memory.

Dosing And Efficacy

  • Administered via single 0.5 mL intramuscular or subcutaneous injection.
  • Requires minimum age of 2 years due to low immunogenicity in infants.
  • Initial efficacy approaches 69% in first year.
  • Cumulative efficacy declines to 55% at 3 years.
  • Mandates revaccination every 3 years for sustained protection.

Safety Profile

  • Mild local pain and swelling frequently observed.
  • Safe for immunocompromised individuals including human immunodeficiency virus infected patients.

Typhoid Conjugate Vaccine (TCV)

Mechanism And Advantages

  • Links Vi-polysaccharide to carrier proteins like Tetanus Toxoid, Diphtheria Toxoid, or CRM197.
  • Transforms T-independent polysaccharide into T-dependent antigen.
  • Triggers T-cell dependent humoral responses.
  • Generates strong anamnestic response and immune memory.
  • Induces herd immunity.

Administration And Efficacy

  • Administered as single 0.5 mL intramuscular dose.
  • Approved for infants starting at 6 months.
  • Demonstrates superior efficacy of 80-85% spanning multiple years.

Formulations Available

  • Typbar-TCV utilizes Tetanus Toxoid carrier.
  • Typhibev incorporates CRM197 carrier.
  • Zyvac TCV employs Tetanus Toxoid carrier.

Live Attenuated Oral Vaccine (Ty21a)

Characteristics

  • Utilizes genetically stable mutant S. Typhi Ty21a strain.
  • Stimulates intestinal mucosal immunity.
  • Administered as enteric-coated capsules.

Limitations

  • Inappropriate for young children due to intact swallowing requirement.
  • Concurrent antibiotics interfere with immune response.
  • Requires revaccination every 3 years.
  • Currently unavailable in India.

Current Guidelines

Routine Immunization Recommendations

  • TCV preferred over Vi-polysaccharide across all ages.
  • Initiated as single dose at 6 months of age.
  • Catch-up immunization recommended up to 18 years.
  • Booster doses lack sufficient evidence for routine recommendation.

Future Innovations

Bivalent Conjugate Vaccines

  • Designed to concurrently target Salmonella Typhi and Salmonella Paratyphi A.
  • Integrates Vi-conjugate with O:2 specific polysaccharide conjugate.
  • Addresses escalating paratyphoid fever incidence across Asia.
  • Preclinical evaluations exhibit robust immunogenicity against both target pathogens.
  • Phase 1 clinical trials currently ongoing to evaluate safety and dose-response profiles.

Backlinks

Graph View