Vi Capsular Polysaccharide Typhoid Vaccine is a sterile solution containing the purified cell surface Vi polysaccharide extracted from Salmonella enterica serovar Typhi (S. Typhi), strain Ty2. It is a subunit vaccine that induces a T-cell independent immune response, primarily producing IgG antibodies against the Vi capsular antigen. This provides protection against typhoid fever caused by Vi-positive strains of S. Typhi. It is indicated for active immunization in individuals two years of age and older. The protection is not lifelong; revaccination is recommended every 3 years for individuals at continued risk.
Adult: A single 0.5 mL intramuscular injection containing 25 mcg of Vi polysaccharide.
Note: 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.
The Vi polysaccharide vaccine is composed of long chains of repeating units of a sugar (N-acetylgalactosaminuronic acid) that is a major component of the protective capsule of S. Typhi. Upon intramuscular injection, the polysaccharide antigen is taken up by antigen-presenting cells and presented to B-lymphocytes. Being a T-cell independent antigen (Type 2), it directly stimulates mature B-cells without significant T-helper cell involvement. This leads to the proliferation and differentiation of B-cells into plasma cells that secrete specific anti-Vi IgG antibodies. These antibodies opsonize the bacteria, facilitating phagocytosis and complement-mediated lysis, thereby preventing invasive disease.
Pregnancy: Category B2: Animal reproduction studies have not been conducted. It is not known whether the vaccine can cause fetal harm. Use during pregnancy only if clearly needed, such as for essential travel to a high-risk area. Ideally, administer before pregnancy or postpone until the second or third trimester if possible.
Driving: Vaccine side effects like dizziness or syncope may impair the ability to drive or operate machinery. Patients should be cautioned.
| Immunosuppressants (e.g., corticosteroids, cyclosporine, tacrolimus, chemotherapeutic agents, radiation therapy) | May diminish the immunological response to the vaccine, potentially leading to suboptimal protection. | Major |
| Other Vaccines (e.g., Yellow Fever, Hepatitis A, Cholera, Japanese Encephalitis) | Can be administered simultaneously at different injection sites without significant interference. Slightly reduced antibody responses to some vaccines have been noted but are not clinically significant. | Moderate |
| Anticoagulants (e.g., warfarin) | Increased risk of bleeding or hematoma at the injection site. Use a fine needle (23 gauge or smaller) and apply firm pressure for at least 2 minutes. | Moderate |