1. Clinical Overview
Salmonella Typhi Vaccine (5mcg) is a purified Vi capsular polysaccharide vaccine for active immunization against typhoid fever caused by Salmonella enterica serovar Typhi. It is a subunit vaccine containing the Vi antigen, which is a key virulence factor of the bacterium. It induces a T-cell independent immune response, primarily producing IgG antibodies that prevent bacterial invasion by blocking attachment and complement-mediated killing. It is a critical public health tool in endemic regions like India.
| Onset | Duration | Bioavailability |
|---|---|---|
| Protective antibody levels are typically achieved within 7-14 days post-vaccination. | Protection lasts for approximately 3 years. Revaccination is recommended every 3 years for continued risk. | Not applicable (Parenteral administration). |
2. Mechanism of Action
The vaccine contains the purified Vi (virulence) capsular polysaccharide antigen of Salmonella Typhi. Upon intramuscular injection, the antigen is taken up by antigen-presenting cells and presented to B-lymphocytes in a T-cell independent manner. This stimulates the proliferation and differentiation of specific B-cell clones into plasma cells that secrete anti-Vi IgG antibodies. These circulating antibodies bind to the Vi capsule on invading Salmonella Typhi bacteria, facilitating opsonization and complement-mediated bacteriolysis, thereby preventing systemic infection.
3. Indications & Uses
- Active immunization against typhoid fever caused by Salmonella Typhi in adults and children ≥2 years of age.
- Prophylaxis for individuals traveling to or residing in typhoid-endemic areas, including many parts of India.
4. Dosage & Administration
Adult Dosage: Single 0.5 mL intramuscular injection containing 5mcg of purified Vi polysaccharide.
Administration: For intramuscular use only, preferably in the deltoid muscle. Do not administer intravenously, intradermally, or subcutaneously. Shake the vial or pre-filled syringe well before use. Use a separate, sterile syringe and needle for each patient. Observe for syncope for 15 minutes post-vaccination.
5. Side Effects
Common side effects may include:
- Pain, tenderness, redness, or induration at the injection site (up to 40%).
- Low-grade fever (<38°C).
- Headache.
- Malaise, myalgia.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Immunosuppressants (e.g., corticosteroids, chemotherapy, biologics) | Diminished antibody response to the vaccine. | Major |
| Anticoagulants (e.g., warfarin) | Increased risk of bleeding or hematoma at injection site. | Moderate |
| Other Vaccines (e.g., Yellow Fever, Hepatitis A) | No clinically significant interaction. Can be administered simultaneously at different sites. | Minor |
7. Patient Counselling
- Do inform the doctor about any allergies, especially to vaccine components or previous vaccines.
- Do report if you are pregnant, planning pregnancy, or breastfeeding.
- Do keep a record of your vaccination date and brand.
- Don't take the vaccine if you have a high fever or severe illness on the day of vaccination.
- Don't rub the injection site vigorously.
8. Toxicology & Storage
Overdose: Unlikely due to single-dose administration in a pre-filled syringe. Theoretical overdose could exacerbate local and systemic reactions (e.g., severe pain, high fever, pronounced malaise).
Storage: Store between +2°C to +8°C (refrigerator). Do not freeze. Protect from light. Do not use if frozen. Keep the vial/syringe in the outer carton. Use immediately after opening. Do not use after the expiry date. Transport in a cold chain.