What is the recommended dosing schedule for typhoid conjugate (TC) injectable vaccine, including booster doses, for food handlers?

Typhoid Conjugate Vaccine Dosing for Food Handlers

For food handlers requiring typhoid conjugate vaccine (TCV), administer a single intramuscular dose, with booster doses recommended every 2-3 years under conditions of continued occupational exposure.

Primary Vaccination Schedule

A single dose of typhoid conjugate vaccine is sufficient for initial protection in food handlers. 1 The modern TCV formulation (Vi-polysaccharide conjugated to protein carrier) requires only one dose to achieve robust immunity, unlike older parenteral inactivated vaccines that required two doses separated by ≥4 weeks. 2

• Dosing: Single 0.5 mL intramuscular injection containing 25 μg of Vi-conjugate 3
• Onset of protection: Immunity develops within 42 days of vaccination 3, 1
• Initial efficacy: Seroconversion rates reach 97-100% after a single dose 3, 1

Booster Dose Recommendations

The critical consideration for food handlers is that vaccine protection wanes significantly after 3-5 years, necessitating regular boosters for sustained occupational protection.

Timing of Boosters

• Every 2-3 years is recommended for continued occupational exposure 2
  • The older ACIP guidelines for parenteral inactivated vaccines specified boosters every 3 years under conditions of repeated exposure 2
  • Recent evidence shows TCV protection declines substantially by years 3-5, with vaccine effectiveness dropping from 84% to 50-55% 4

Important Caveats About Booster Timing

• A single booster dose is sufficient even if more than 3 years have elapsed since prior vaccination 2
• Age at initial vaccination matters: Adults maintain immunity longer than children vaccinated before age 2 years, who show the fastest waning (vaccine effectiveness dropping to 24% by years 3-5) 4
• For food handlers initially vaccinated as adults, the standard 3-year booster interval is appropriate 2

Practical Algorithm for Food Handler Vaccination

1. Initial vaccination: Single TCV dose (0.5 mL IM) 3, 1
2. First booster: 2-3 years after initial dose 2, 4
3. Subsequent boosters: Every 2-3 years while occupational exposure continues 2
4. If booster is overdue: Give single booster dose regardless of time elapsed 2

Key Advantages of TCV Over Older Vaccines

• Superior immunogenicity: TCV produces geometric mean titers of 1293 compared to 411 with older Vi polysaccharide vaccines 1
• Better tolerability: Significantly fewer systemic reactions compared to older parenteral vaccines that caused fever in 14-29% and severe local reactions in 6-40% of recipients 2
• Longer-lasting antibodies: Anti-Vi IgG titers remain higher at 2 years (GMT 82) with better avidity (60%) compared to older vaccines 1
• Single-dose convenience: Unlike the 4-dose oral Ty21a vaccine that requires refrigeration and specific timing 2

Common Pitfalls to Avoid

• Do not use oral live-attenuated Ty21a vaccine in immunocompromised food handlers 2
• Do not delay boosters beyond 3 years in high-risk occupational settings, as protection wanes significantly 4
• Do not confuse TCV with older Vi polysaccharide vaccines that had different booster schedules (every 3 years was based on older vaccine data) 2
• Ensure proper storage and administration: TCV is given intramuscularly, not subcutaneously like some older formulations 2, 3