What are the indications, dosing schedule, contraindications, and alternative options for the typhoid injection (Vi polysaccharide vaccine)?

Typhoid Injection: Indications, Dosing, and Recommendations

The typhoid Vi polysaccharide injection (Typhim Vi) should be given as a single 0.5 mL intramuscular dose to adults and children ≥2 years of age, at least 2 weeks before travel to endemic areas, with boosters every 2 years under continued exposure. 1

Who Should Receive the Typhoid Injection

The Vi polysaccharide vaccine is not recommended for routine use in the United States but is specifically indicated for 1:

• Travelers to endemic regions (Africa, Asia, Central/South America) with prolonged exposure to potentially contaminated food and water
• Household contacts of documented typhoid carriers with intimate, continued exposure
• Laboratory workers who frequently handle S. typhi

Do not use for 2, 1:

• Common-source outbreak control
• Post-natural disaster settings
• Rural summer camp attendees
• Routine sewage workers (unless in endemic areas)

Dosing Schedule

Primary Vaccination

• Adults and children ≥2 years: 0.5 mL (25 μg) intramuscularly as a single dose 1
• Administer at least 2 weeks before expected exposure 1

Booster Dosing

• Every 2 years under conditions of repeated or continued exposure 1
• A single booster dose is sufficient even if >2 years have elapsed 1

Efficacy Profile

The Vi polysaccharide vaccine demonstrates strong first-year protection that wanes over time:

• Year 1: 69% efficacy (95% CI: 63-74%) 3
• Year 2: 59% efficacy (95% CI: 45-69%), with more variable results 3
• 3-year cumulative: Approximately 55% efficacy 3

Critical caveat: Vaccination is not a substitute for careful food and water selection, as vaccine protection can be overwhelmed by large bacterial inocula 2, 1

Safety and Adverse Events

The Vi polysaccharide vaccine is significantly better tolerated than older whole-cell vaccines 4:

Common reactions (more frequent than placebo) 3:

• Pain at injection site (moderate-certainty evidence)
• Swelling at injection site (moderate-certainty evidence)

Not increased compared to placebo 3:

• Fever (moderate-certainty evidence)
• Erythema (low-certainty evidence)

In direct comparison studies, only 18.6% of Vi vaccine recipients reported local reactions versus 59.7% with whole-cell vaccine on day 1 (P<0.001) 4. Systemic reactions occurred in 3.4% versus 7.9% respectively 4.

No serious adverse events have been reported in randomized controlled trials 3.

Contraindications

Absolute contraindication 1:

• History of hypersensitivity to any vaccine component

Relative considerations (no data available):

• Pregnancy: No safety data exists; use clinical judgment 2
• Age <2 years: Not approved for this age group 1

Alternative Vaccine Options

Oral Ty21a Vaccine (Vivotif)

• Dosing: 4 enteric-coated capsules taken on alternate days with cool liquid 1 hour before meals 2
• Efficacy: 50% cumulative efficacy over 2.5-3 years 3
• Advantages: Similar efficacy with fewer adverse reactions than parenteral vaccines 2
• Disadvantages: Requires refrigeration, all 4 doses needed for maximum efficacy, contraindicated in immunocompromised patients 2
• Booster: Repeat 4-dose series every 5 years 2

Typhoid Conjugate Vaccines (TCVs)

Newer conjugate vaccines (Vi-TT, Vi-rEPA) show promise:

• Vi-rEPA: 94% efficacy in year 1,87% in year 2 in children 2-5 years 3
• Vi-TT (Typbar-TCV): WHO-recommended as preferred vaccine, though field efficacy data still emerging 3, 5
• Advantages: May provide longer-lasting immunity, suitable for children ≥6 months, better immunological memory 5, 6

Key Clinical Pitfalls

1. Timing error: Administering vaccine <2 weeks before travel reduces protection 1
2. False security: Patients must understand vaccination does not eliminate need for food/water precautions 2, 1
3. Booster neglect: Protection wanes significantly after 2 years; ensure timely boosters for ongoing exposure 1
4. Age restriction: Do not use in children <2 years; consider oral Ty21a or conjugate vaccines for this age group if available 1
5. Misuse for treatment: This vaccine does not treat active typhoid fever or chronic carrier states 1

Concurrent Administration

The Vi polysaccharide vaccine may be administered simultaneously with meningococcal conjugate vaccine (Menactra) at different injection sites without affecting immunogenicity or tolerability 1.