What are the current recommendations for typhoid vaccination, including indicated populations (travelers to endemic areas, laboratory personnel, residents of endemic regions), available formulations (injectable Vi polysaccharide vaccine and oral live‑attenuated Ty21a vaccine), dosing schedules, booster intervals, and contraindications (immunocompromised state, pregnancy, severe allergy, age <2 years)?

Typhoid Vaccine Recommendations

Indicated Populations

Typhoid vaccination should be administered to travelers visiting endemic areas (particularly Latin America, Asia, and Africa), laboratory workers handling S. typhi, and household contacts of documented typhoid carriers. 1, 2

• Travelers to endemic regions require vaccination at least 2 weeks before departure, especially those with prolonged exposure to potentially contaminated food and water in developing countries 1, 3
• Microbiology laboratory personnel who frequently work with S. typhi should receive vaccination due to documented occupational transmission risk (seven laboratory-acquired cases reported during 1985-1994) 4, 1
• Household contacts with intimate exposure to documented typhoid carriers warrant vaccination 1, 2
• Typhoid vaccination is not indicated for routine use in the United States, common source outbreaks, natural disasters, or rural summer camps 1, 2

Available Vaccine Formulations

Vi Polysaccharide Vaccine (Injectable)

• Single-dose intramuscular or subcutaneous injection of 0.5 mL for adults and children ≥10 years 1, 3
• For children 6 months to <10 years: 0.25 mL subcutaneously given on two occasions separated by ≥4 weeks 3
• Efficacy: 69% in year 1 (high-certainty evidence), declining to 59% in year 2, with three-year cumulative efficacy around 55% 5, 3
• Booster interval: Every 2 years under conditions of continued or repeated exposure 1, 3

Ty21a Oral Live-Attenuated Vaccine

• Four enteric-coated capsules taken on alternate days (total 7-day course) with cool liquid no warmer than 37°C, approximately 1 hour before meals 2, 3
• Approved for adults and children >6 years of age 2
• Efficacy: 50% cumulative protection over 2.5-3 years, with long-term data showing 62% protection over 7 years 5, 6
• Booster interval: Complete four-dose series every 5 years 2, 3

Vi-Tetanus Toxoid Conjugate Vaccine (TCV)

• Preferred vaccine according to WHO recommendations due to superior efficacy profile 3
• Single-dose administration with 83% efficacy at 2 years post-immunization (four trials, high-certainty evidence) 7, 3
• Four-year efficacy of 78% for Vi-TT conjugate vaccine 3
• Effective in infants and young children, requiring less frequent boosting than other formulations 3

Dosing Schedules

Primary Immunization

• Vi polysaccharide: Single 0.5 mL dose IM/SC for ages ≥10 years; two doses of 0.25 mL separated by ≥4 weeks for ages 6 months to <10 years 1, 3
• Ty21a oral: Four capsules on alternate days for ages >6 years 2, 3
• TCV: Single dose (when available as first-line choice) 3

Booster Intervals

• Vi polysaccharide: Every 2 years with continued exposure 1, 3
• Ty21a oral: Complete four-dose series every 5 years 2, 3
• The older 1991 guideline suggested 3-year boosters for inactivated vaccine 4, but current FDA labeling and more recent guidelines recommend 2-year intervals 1, 3

Contraindications and Precautions

Vi Polysaccharide Vaccine

• Contraindicated in individuals with history of severe local or systemic reaction to previous dose 1, 4
• Should not be used in immunocompromised patients or those with HIV due to inadequate immune response 3
• Minimum age: 2 years (though can be given at 6 months with modified dosing) 1, 3

Ty21a Oral Vaccine

• Contraindicated in immunocompromised persons, including those with asymptomatic HIV infection 2, 4
• Not recommended for children <6 years of age 2, 4
• Not recommended during pregnancy (live-attenuated vaccine) 4
• Theoretical concerns exist regarding concurrent use with antimicrobials (including antimalarial chemoprophylaxis), viral vaccines, or immune globulin, which may reduce immunogenicity 4

General Contraindications

• Severe allergic reaction to vaccine components 1, 2
• Age <2 years for Vi polysaccharide (standard dosing) and <6 years for Ty21a 1, 2

Safety Profile

Vi Polysaccharide Vaccine

• Local reactions: Injection site pain and swelling are common 5, 3
• Systemic effects: Fever is probably not increased compared to placebo 5
• Serious adverse events are rare (0.47-1.3 per 100,000 doses during 1994-1999, with no deaths) 4

Ty21a Oral Vaccine

• Excellent safety profile with adverse event rates <1/100,000 doses and comparable to placebo 5, 3
• May cause mild gastrointestinal symptoms (nausea, abdominal cramps, vomiting) at rates <1/100,000 4
• Fever may be slightly more common than placebo 5

Critical Clinical Caveats

• Vaccination is not a substitute for food and water precautions, as vaccines provide only 50-80% protection and can be overwhelmed by large bacterial inocula 1, 2, 3
• Neither vaccine protects against Salmonella Paratyphi or other enteric pathogens 2, 4
• Vaccines cannot treat acute typhoid infection or chronic carrier states 1, 2
• TCV should be first-line choice when available due to superior long-term protection, effectiveness in young children, and less frequent boosting requirements 3
• If TCV is unavailable, Vi polysaccharide is the alternative for ages ≥2 years, with Ty21a reserved for ages >6 years 3