How long is the typhoid (Salmonella Typhi) vaccine effective?

Duration of Typhoid Vaccine Protection

The typhoid vaccine provides protection for different durations depending on the type: the oral live-attenuated Ty21a vaccine is effective for approximately 5 years, while the parenteral inactivated typhoid vaccine provides protection for approximately 2-3 years. 1

Types of Typhoid Vaccines and Their Duration of Protection

There are two main types of typhoid vaccines currently available:

1. Oral Live-Attenuated Ty21a Vaccine:

   • Administered as four enteric-coated capsules taken on alternate days
   • Protection Duration: Approximately 5 years
   • Efficacy: 50-80%
   • Booster recommendation: Revaccination with the entire four-dose series every 5 years 2, 1
   • Long-term studies have shown that the protection remains strong throughout the 5-year period 3

2. Parenteral Inactivated Typhoid Vaccine:

   • Administered as a single 0.5 mL intramuscular injection
   • Protection Duration: Approximately 2-3 years
   • Efficacy: 51-76%
   • Booster recommendation: Booster doses should be given every 3 years to persons with continued or repeated exposure 2, 1

Evidence for Duration of Protection

The duration of protection has been established through multiple field trials:

• For the oral Ty21a vaccine, surveillance data from field trials in Santiago, Chile showed that three doses of the enteric-coated capsule formulation conferred 67% protection over three years and 62% protection over seven years of follow-up 3

• For the liquid formulation of Ty21a (which is less commonly used), protection was 77% over three years and 78% over five years 3

• For the parenteral inactivated vaccine, efficacy is highest in the first year after vaccination (69%) and declines somewhat in the second year (59%) 4

Recommendations for Booster Doses

Based on the established duration of protection:

• For Oral Ty21a Vaccine: Revaccination with the entire four-dose series is recommended every 5 years for individuals with continued or repeated exposure to S. typhi 2, 1

• For Parenteral Inactivated Vaccine: Booster doses should be administered every 3 years for individuals with continued or repeated exposure 2

Who Needs Typhoid Vaccination

Typhoid vaccination is recommended for:

• Travelers to areas with recognized risk of S. typhi exposure, particularly those visiting developing countries in Latin America, Asia, and Africa
• Persons with intimate exposure to documented typhoid carriers
• Laboratory workers who frequently work with S. typhi 2, 1

Important Considerations

• Neither vaccine provides 100% protection, so careful food and water selection remains important even after vaccination 2
• The efficacy of typhoid vaccines may be overwhelmed by large inocula of S. typhi 2
• Newer typhoid conjugate vaccines (TCVs) are being developed and may provide longer-lasting immunity, but data suggests that immunity may still wane after five years, especially in children under two 5

Remember that typhoid vaccination is just one component of typhoid prevention. Careful selection of food and water in endemic areas remains essential even after vaccination.