What are the recommended typhoid vaccination options, dosing schedules, contraindications, and booster intervals for individuals aged 2 years and older?

Typhoid Immunization Recommendations

For individuals aged 2 years and older requiring typhoid vaccination, choose either oral Ty21a vaccine (4 capsules over alternate days) or injectable Vi polysaccharide vaccine (single 0.5 mL dose), with boosters every 5 years for oral and every 3 years for injectable formulations.

Vaccine Options and Primary Dosing

Oral Live-Attenuated Ty21a Vaccine

• Dosing schedule: 4 enteric-coated capsules taken on alternate days (days 1,3,5,7) 1
• Administration: Take with cool liquid no warmer than 37°C (98.6°F), approximately 1 hour before meals 1
• Storage: Must be refrigerated; all 4 doses required for maximum efficacy 1
• Age range: Approved for children ≥2 years and adults 1
• Efficacy: Prevents approximately 50% of typhoid cases over 2.5-3 years (moderate-certainty evidence) 2

Injectable Vi Polysaccharide Vaccine

• Adults and children ≥10 years: 0.5 mL subcutaneously as 2 doses separated by ≥4 weeks 1
• Children 2-10 years: 0.25 mL subcutaneously as 2 doses separated by ≥4 weeks 1
• Efficacy: Prevents 69% of cases in year 1 (high-certainty evidence), 59% in year 2 (moderate-certainty evidence) 2
• Accelerated schedule: If insufficient time, give 3 doses at weekly intervals (less effective) 1

Booster Intervals

For Parenteral (Injectable) Vaccines

• Booster every 3 years under conditions of continued or repeated exposure 1
• Single booster dose sufficient even if >3 years have elapsed 1
• Dosing for boosters:
  • Adults and children ≥10 years: 0.5 mL subcutaneously or 0.1 mL intradermally 1
  • Children 2-10 years: 0.25 mL subcutaneously or 0.1 mL intradermally 1

For Oral Ty21a Vaccine

• Revaccination with entire 4-dose series every 5 years 1
• Field data showed continued efficacy 5 years post-vaccination 1
• Recent evidence suggests immunity may wane after 5 years, especially in children under 2 3

Indications for Vaccination

Selective vaccination is indicated for 1:

1. Travelers to endemic areas (Latin America, Asia, Africa) with prolonged exposure to potentially contaminated food/water
2. Household contacts of documented typhoid carriers
3. Laboratory workers frequently handling S. typhi
4. Sewage workers only in endemic areas

Not indicated for: Common-source outbreak control, rural summer camps, natural disaster areas 1

Contraindications and Precautions

Oral Ty21a Vaccine

• Contraindicated in:
  • Immunocompromised persons, including HIV-infected individuals 1
  • Pregnancy (no safety data available) 1
• Side effects: Rare; abdominal discomfort, nausea, vomiting, rash occurred at same frequency as placebo 1, 2

Injectable Vi Polysaccharide Vaccine

• Contraindicated: History of severe local or systemic reactions to previous dose 1
• Use with caution: Pregnancy (no safety data, but theoretically safer than live vaccine for immunocompromised) 1
• Common adverse effects 1, 2:
  • Fever: 14-29% of recipients
  • Headache: 9-30%
  • Severe local pain/swelling: 6-40%
  • Work/school absence: 13-24%

Important Clinical Caveats

Critical warning: Typhoid vaccination is not a substitute for careful food and water selection—vaccines are not 100% effective and protection can be overwhelmed by large inocula of S. typhi 1, 4.

Avoid acetone-inactivated vaccine by intradermal route due to severe local reactions 1.

Newer conjugate vaccines (Vi-TT, Vi-rEPA): While showing promise with 87-94% efficacy in limited trials 2, 5, the evidence base remains insufficient compared to established Ty21a and Vi polysaccharide vaccines. The WHO-prequalified Typbar-TCV requires ongoing field evaluation 2, 6.

Age considerations: Limited data exists for children <2 years with traditional vaccines 2. For adults >55 years and pregnant women, no trial data is available 2.