What is the recommended dosing schedule for the oral typhoid vaccine, Ty21a (Salmonella Typhi vaccine)?

Recommended Dosing Schedule for Oral Typhoid Vaccine (Ty21a)

The recommended dosing schedule for the oral typhoid vaccine Ty21a (Salmonella Typhi vaccine) is one enteric-coated capsule taken on alternate days (days 1,3,5, and 7) for a total of four capsules, with each capsule taken approximately 1 hour before a meal with a cold or lukewarm drink not exceeding body temperature (37°C/98.6°F).

Administration Details

• Each capsule should be swallowed whole (not chewed) approximately 1 hour before a meal 1
• The capsules must be taken with a cold or lukewarm drink not exceeding body temperature 1
• The complete vaccination series consists of 4 capsules taken on alternate days (e.g., days 1,3,5, and 7) 2, 1
• Immunization should be completed at least 1 week prior to potential exposure to S. typhi 1
• The vaccine must be stored under refrigeration between 2°C and 8°C (35.6°F - 46.4°F) at all times, including between doses 1

Important Considerations

Contraindications

• Not recommended for children under 6 years of age 2, 3, 1
• Contraindicated in immunocompromised persons, including those with HIV infection 3, 1
• Should not be administered to pregnant women 2

Drug Interactions

• Should not be administered to persons receiving antimicrobial agents until >24 hours after any antibiotic dose 3
• Antimalarial drugs with antibacterial activity may interfere with vaccine immunogenicity:
  • Mefloquine and chloroquine can be administered together with Ty21a 1
  • Proguanil should be administered only if 10 days or more have elapsed since the final dose of Ty21a 1

Booster Recommendations

• Re-immunization is recommended every 5 years for individuals who remain at risk of typhoid fever exposure 2, 1
• The booster dose consists of the same 4-capsule regimen taken on alternate days 1
• Studies have shown that protection lasts for at least 5 years after the initial vaccination series 4

Efficacy

• When properly administered, the 4-dose regimen provides approximately 67% protection against laboratory-confirmed typhoid infection for at least 4-7 years 3, 4
• Fewer doses confer less protection - studies show that one dose provides only 29% efficacy while two doses provide about 59% efficacy for the first two years 5
• Compliance with the proper administration schedule is crucial for maximum efficacy 6

Common Pitfalls to Avoid

• Failure to complete all 4 doses - this significantly reduces vaccine effectiveness 5
• Taking capsules after meals instead of 1 hour before meals 6
• Not maintaining the alternate-day schedule 6
• Failure to keep the vaccine refrigerated between doses 6
• Chewing the capsules instead of swallowing them whole 1
• Using water that exceeds body temperature to swallow the capsule 1

Following this dosing schedule carefully will help ensure optimal protection against typhoid fever for travelers to endemic areas, individuals with exposure to typhoid carriers, and laboratory workers who frequently work with S. typhi.