Points to Ponder for NEET-PG, FMGE & NEXT
- Vi polysaccharide vaccine is purified capsular polysaccharide from Salmonella Typhi strain Typhi 2.
- Ty21a oral vaccine is from live attenuated S. Typhi strain Ty21a (lacks UDP-galactose 4-epimerase enzyme – Gal E mutant).
- Vi polysaccharide vaccine is preferred for rapid protection in travelers.
- Ty21a oral vaccine offers longer-lasting immunity for endemic areas or frequent travel.
Two main types of typhoid vaccines are available:
Vi polysaccharide vaccine (TYPHIM Vi Vaccine):
- Composition: Purified Vi capsular polysaccharide from Salmonella Typhi strain Typhi 2.
- Administration:
- Single dose subcutaneously or intramuscularly.
- Not recommended for children under 2 years old.
- Onset of protection: 7 days after vaccination.
- Duration of protection: Up to 3 years (revaccination recommended).
- Safety:
- No serious systemic or local side effects reported.
- Contraindicated only in case of hypersensitivity to the vaccine components.
- Advantages:
- Excellent for travelers due to single-dose regimen and rapid onset of protection.
- Can be co-administered with other travel vaccines.
- Disadvantages:
- Does not provide long-term protection as compared to the oral vaccine.
- Not recommended for young children.
Ty21a oral vaccine (TYPHORAL Vaccine):
- Composition: Live attenuated S. Typhi strain Ty21a (lacks UDP-galactose 4-epimerase enzyme – Gal E mutant).
- Administration:
- Three doses (on days 1, 3, and 5) orally.
- Not recommended for individuals with immunodeficiency or gastrointestinal diseases that might affect absorption.
- Onset of protection: 7 days after the last dose.
- Duration of protection:
- Up to 3 years for people in endemic areas.
- Annual vaccination recommended for travelers from non-endemic to endemic regions.
- Safety:
- Generally well-tolerated with mild side effects like abdominal discomfort or bloating.
- Not recommended for pregnant or breastfeeding women.
- Advantages:
- Provides longer-lasting immunity compared to the Vi polysaccharide vaccine.
- May offer some protection against other Salmonella serotypes.
- Disadvantages:
- Requires a three-dose regimen over several days.
- Not suitable for all individuals due to potential contraindications.
