What it's for (Indications)
- Typhoid vaccine is indicated for active immunization against typhoid fever caused by *Salmonella Typhi*.
- It is primarily recommended for individuals at increased risk of exposure to *S.
- Typhi*.
- This includes travelers visiting areas where typhoid fever is endemic or epidemic, such as parts of Asia, Africa, and Latin America.
- Additionally, the vaccine is advised for individuals in close contact with *S.
- Typhi* carriers and for laboratory personnel who routinely work with *S.
- Typhi* cultures.
- Both injectable inactivated (Vi capsular polysaccharide) and oral live attenuated forms of the vaccine are available, each with specific age recommendations and administration schedules.
- Vaccination should be considered a critical component of a comprehensive prevention strategy, alongside strict adherence to food and water safety precautions, especially in high-risk environments.
- The vaccine is not intended for the treatment of acute typhoid fever.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Dosage varies depending on the vaccine type and formulation. For the **injectable Vi capsular polysaccharide vaccine** (e.g., Typhim Vi, Typherix), the standard adult and pediatric dose (for individuals aged 2 years and older) is a single 0.5 mL intramuscular injection. This dose should be administered at least 2 weeks prior to potential exposure to allow for adequate immune response development. A booster dose is typically recommended every 2 to 3 years for individuals who remain at continued risk of exposure. For the **oral live attenuated Ty21a vaccine** (e.g., Vivotif), the standard regimen consists of 4 capsules, taken orally on alternate days (e.g., Days 1, 3, 5, 7). Each capsule must be swallowed whole, not chewed, with cool liquid, approximately one hour before a meal. The full series of 4 doses should be completed at least one week before potential exposure. A booster regimen (another 4-dose series) is generally recommended every 5 years for continuous protection in adults and children aged 6 years and older. Specific dosing instructions should always be consulted from the manufacturer's prescribing information and adjusted based on individual patient factors and local guidelines. |
Safety & Warnings
Common Side Effects
- Common side effects associated with typhoid vaccines are generally mild and transient.
- For the **injectable Vi capsular polysaccharide vaccine**, local reactions at the injection site are most frequent, including pain, tenderness, redness (erythema), and swelling (induration).
- Systemic reactions may include headache, malaise, low-grade fever, myalgia (muscle aches), and nausea.
- For the **oral live attenuated Ty21a vaccine**, gastrointestinal side effects are common due to its oral administration, such as abdominal discomfort, nausea, vomiting, diarrhea, and constipation.
- Other systemic reactions can include headache, fever, and rash.
- Serious adverse events, such as severe allergic reactions (e.
- g.
- , anaphylaxis), are rare but possible with any vaccine.
- Patients should be advised to seek immediate medical attention if they experience symptoms of a severe allergic reaction (e.
- g.
- , difficulty breathing, hives, swelling of the face or throat, dizziness).
- All adverse events, particularly serious ones, should be reported to the appropriate regulatory bodies.
Serious Warnings
- Black Box Warning: While typhoid vaccines do not carry a formal FDA Black Box Warning, it is crucial to recognize specific serious safety considerations, particularly concerning the live attenuated oral vaccine. For the oral live attenuated typhoid vaccine (e.g., Vivotif), there is a significant risk of disseminated infection in individuals who are immunocompromised. This includes patients with congenital or acquired immunodeficiency states, those receiving immunosuppressive therapies such as high-dose corticosteroids, alkylating agents, antimetabolites, or radiation therapy, and individuals with HIV/AIDS. Administration of live attenuated vaccines to these populations can lead to severe and potentially fatal outcomes. Healthcare providers must thoroughly assess the immune status of prospective vaccine recipients before administering the oral live attenuated vaccine. In such cases, the injectable inactivated Vi polysaccharide vaccine may be a safer alternative, though its efficacy can also be diminished in immunocompromised individuals. Additionally, severe allergic reactions, including anaphylaxis, can occur after any vaccine administration, necessitating the immediate availability of appropriate medical treatment and close observation post-vaccination.
- Typhoid vaccines, while effective, do not provide 100% protection against typhoid fever, emphasizing the continued importance of practicing strict food and water safety precautions, especially in endemic areas.
- For the **oral live attenuated Ty21a vaccine**, particular caution is advised.
- It should not be administered to individuals experiencing acute febrile illness, severe gastrointestinal illness with vomiting or diarrhea, or those with known immunodeficiency or immunosuppression (e.
- g.
- , due to HIV/AIDS, leukemia, lymphoma, generalized malignancy, or treatment with corticosteroids, alkylating agents, antimetabolites, or radiation therapy), as there is a theoretical risk of disseminated infection in these populations.
- The efficacy of the oral vaccine may also be reduced if co-administered with certain antibiotics or antimalarial drugs; prescribers should consult specific drug interaction information.
- For both vaccine types, vaccination should be postponed in individuals with acute moderate or severe illness.
- Neither vaccine is intended for the treatment of active typhoid fever.
- Intravenous administration of any typhoid vaccine is strictly contraindicated.
- Healthcare providers should ensure that appropriate medical treatment for allergic reactions, including epinephrine, is readily available during vaccine administration.
How it Works (Mechanism of Action)
The mechanism of action differs between the two primary types of typhoid vaccines. The **injectable Vi capsular polysaccharide vaccine** contains purified Vi capsular polysaccharide antigen derived from *Salmonella Typhi*. This polysaccharide acts as an immunogen, stimulating the B lymphocytes to produce specific antibodies against the Vi antigen. These antibodies are primarily of the IgG class and play a crucial role in conferring protection by mediating opsonization and phagocytosis of *S. Typhi*, thus preventing invasion and dissemination of the bacteria. This vaccine elicits a T-cell-independent immune response and does not cause typhoid disease as it contains no live bacteria. The **oral live attenuated Ty21a vaccine** contains a live, but genetically modified, avirulent strain of *Salmonella Typhi*. Upon oral administration, this attenuated strain colonizes the gastrointestinal tract and undergoes limited replication, mimicking a natural infection without causing overt disease. This process stimulates both systemic humoral (antibody, primarily IgG and IgM) and cellular immune responses, as well as local mucosal immunity, particularly secretory IgA antibodies in the intestinal lining. These immune responses contribute to protection by preventing *S. Typhi* from adhering to and invading the intestinal epithelium.