What is the difference between Typhoid Conjugate Vaccine (TCV) and Vi polysaccharide vaccine for typhoid protection?

Typhoid Conjugate Vaccine (TCV) vs Vi Polysaccharide Vaccine

The typhoid conjugate vaccine (TCV) is superior to Vi polysaccharide vaccine and should be the preferred choice for typhoid prevention, offering higher efficacy (78% at 4 years vs 55% at 3 years), longer duration of protection, effectiveness in children under 2 years, and sustained immune responses without the need for frequent boosters. 1

Key Efficacy Differences

TCV (Vi-Tetanus Toxoid Conjugate)

• Four-year efficacy: 78% - substantially higher than Vi polysaccharide 1
• Maintains protective antibody levels for longer periods due to T-cell dependent immune response 2
• Single dose provides robust protection across all age groups including infants ≥6 months 3
• Induces immunologic memory, allowing for effective booster responses 4

Vi Polysaccharide Vaccine

• Three-year cumulative efficacy: approximately 55% 1, 5
• Year 1 efficacy is strong at 69% (95% CI 63-74%) 5
• Year 2 efficacy drops to 59% (95% CI 45-69%) with more variable results 5
• Antibody titers decline more rapidly compared to TCV 2
• Requires boosters every 2-3 years for continued protection 6, 1

Age-Specific Considerations

Children Under 2 Years

• TCV is effective in infants ≥6 months, achieving 98% seroconversion with GMT of 1937 1, 3
• Vi polysaccharide vaccine is not licensed for children under 2 years due to poor immunogenicity in this age group 6, 7
• This represents a critical advantage for TCV in endemic areas where young children face highest typhoid risk 3

Children 2-5 Years and Adults

• Both vaccines work in this population, but TCV demonstrates superior long-term protection 1, 5
• At 2 years post-vaccination, TCV recipients maintain GMT of 82 with 60% antibody avidity vs Vi polysaccharide GMT of 46 with 46% avidity 3

Immunologic Mechanisms Explaining TCV Superiority

The conjugation of Vi polysaccharide to tetanus toxoid converts a T-cell independent antigen into a T-cell dependent one, fundamentally changing the immune response 4:

• TCV induces multiple IgG subclasses and generates immunologic memory 3, 4
• Vi polysaccharide alone fails to generate memory B cells, requiring more frequent boosting 4
• Both IgM and IgG independently provide protection, but TCV sustains higher antibody levels over time 2
• After 5+ months, differences in tissue bacterial burden protection become apparent, favoring TCV due to better antibody persistence 2

Booster Requirements

TCV

• Single dose provides years of protection without immediate need for boosting 1, 3
• When boosters are given, TCV recipients show robust anamnestic responses across all age groups 3

Vi Polysaccharide

• Requires boosters every 2 years for ongoing risk 6, 7
• More frequent boosting needed compared to TCV due to faster antibody decline 1, 2

Safety Profiles

Both vaccines demonstrate excellent safety with mild, self-limited adverse events 1:

TCV

• Injection site pain and swelling more common than placebo 1
• Fever may occur but is generally mild 1
• No serious vaccine-attributable adverse events reported 3

Vi Polysaccharide

• Injection site swelling and pain more common than placebo 5
• Fever rates similar to placebo 5
• Erythema at injection site may occur 5

Clinical Algorithm for Vaccine Selection

For all patients requiring typhoid vaccination:

1. First choice: TCV (Typbar-TCV) - single dose, all ages ≥6 months 1

   • Provides superior long-term protection
   • Effective in infants and young children
   • Less frequent boosting required

2. Alternative: Vi polysaccharide - only if TCV unavailable, ages ≥2 years 6, 1

   • Single 0.5 mL dose intramuscularly or subcutaneously
   • Plan for boosters every 2 years with continued exposure 6, 7

3. For children 6 months to <2 years: TCV is the only option 1, 3

Important Caveats

• Neither vaccine provides 100% protection - both offer 50-80% efficacy range, which can be overwhelmed by large inocula 6, 1
• No protection against Salmonella Paratyphi A, B, or C - vaccines only target S. Typhi 6, 8
• Vaccination does not replace food and water safety precautions - hand hygiene and avoiding high-risk foods/beverages remain essential 6, 8
• Vi polysaccharide vaccine should not be used in immunocompromised patients or those with HIV 1

Geographic Considerations

Both vaccines are recommended for travelers to endemic areas (Latin America, Asia, Africa) with moderate to high typhoid risk, particularly those with prolonged exposure to potentially contaminated food and water 6, 1, 8. However, TCV's superior efficacy and longer duration make it the preferred choice regardless of destination 1.