When and how should typhoid vaccination be administered, including indications, recommended vaccine formulations, dosing schedule, contraindications, and timing before exposure?

Typhoid Vaccine Administration

Travelers to endemic areas in Latin America, Asia, and Africa should receive typhoid vaccination at least 1 week before departure, with either the oral Ty21a vaccine (4 capsules on alternate days) or the Vi polysaccharide vaccine (single 0.5 mL injection), both providing 50-80% protection. 1

Who Should Be Vaccinated

• Travelers to endemic areas with recognized risk of S. typhi exposure, particularly those visiting developing countries in Latin America, Asia, and Africa with prolonged exposure to potentially contaminated food and water 1
• Laboratory workers (microbiologists) who frequently work with S. typhi cultures 2, 1
• Household contacts of documented typhoid carriers with continued intimate exposure 2, 1

Available Vaccine Formulations

Oral Ty21a Vaccine (Vivotif)

Administration protocol:

• One enteric-coated capsule taken on alternate days (days 1,3,5, and 7) for a total of 4 doses 3
• Must be swallowed whole (not chewed) approximately 1 hour before meals with cool or lukewarm liquid not exceeding 37°C (98.6°F) 3
• Complete immunization at least 1 week prior to potential exposure 3
• Approved for adults and children ≥6 years of age 3

Efficacy:

• Provides 67% protection over 3 years and 62% protection over 7 years 4
• Cumulative efficacy of approximately 50% at 2.5-3 years 5

Booster schedule:

• Revaccination with entire 4-dose series every 5 years under conditions of continued or repeated exposure 3, 1

Vi Polysaccharide Vaccine (Injectable)

Administration protocol:

• Single 0.5 mL dose given subcutaneously or intramuscularly for adults and children ≥10 years 1
• For children 6 months to <10 years: 0.25 mL subcutaneously on two occasions separated by ≥4 weeks 1

Efficacy:

• Year 1: 69% protection (high-certainty evidence) 5
• Year 2: 59% protection (moderate-certainty evidence) 5
• Three-year cumulative efficacy approximately 55% 5, 6

Booster schedule:

• Every 2 years for continued protection with ongoing exposure 1
• Some guidelines suggest every 3 years 2, 7

Typhoid Conjugate Vaccine (TCV)

Efficacy:

• Superior efficacy of 78% at 4 years 1
• Pooled efficacy of 83% at 2 years post-immunization 6
• TCV is recommended as first-line choice when available due to superior long-term protection and less frequent boosting requirements 1

Critical Contraindications and Precautions

Oral Ty21a Vaccine

• Contraindicated in immunocompromised persons, including those with HIV infection 2, 3
• Not recommended for children <6 years of age 2, 3
• Not recommended during pregnancy unless clearly needed 3
• Must be stored refrigerated at 2-8°C (35.6-46.4°F) at all times; vaccine potency depends on proper storage 3

Vi Polysaccharide Vaccine

• Contraindicated with history of severe local or systemic reaction after previous dose 2
• Should not be used in immunocompromised patients or those with HIV due to inadequate immune response 1

Drug Interactions

• Mefloquine and chloroquine can be administered together with oral Ty21a vaccine 3
• Proguanil should only be given if ≥10 days have elapsed since final Ty21a dose 3
• Concurrent antibiotics may interfere with oral vaccine immunogenicity 2, 3

Essential Counseling Points

• Vaccination is NOT a substitute for food and water precautions - vaccines are not 100% effective and protection can be overwhelmed by large bacterial inocula 1, 7
• All 4 doses of oral vaccine must be completed on schedule to achieve maximal protection 3
• Even vaccinated travelers must practice careful food and water selection in endemic areas 2, 1
• Hand hygiene and avoiding high-risk foods/beverages remain essential despite vaccination 1

Common Pitfalls to Avoid

• Timing error: Failing to complete vaccination at least 1 week before travel exposure 3
• Storage failure: Not maintaining refrigeration of oral vaccine between doses, which destroys vaccine potency 3
• Incomplete dosing: Not completing all 4 doses of oral vaccine on the alternate-day schedule 3
• Chewing capsules: Instructing patients to chew rather than swallow oral vaccine capsules whole 3
• False security: Relying solely on vaccination without emphasizing continued food/water safety precautions 1, 7

Adverse Events

Oral Ty21a Vaccine

• Adverse event rates comparable to placebo (<1/100,000 doses) 1
• Mild reactions include nausea, abdominal cramps, vomiting, and skin rash 2
• Fever is more common following vaccination compared to placebo 5

Vi Polysaccharide Vaccine

• Injection site pain and swelling more common than placebo 5
• Fever rates similar to placebo 5
• Rarely causes systemic effects 1
• No serious adverse effects reported in randomized controlled trials 5