Vivotif: Uses, Dosage & Side Effects
A live attenuated oral typhoid vaccine for protection against typhoid fever in adults and children aged 5 years and older
Vivotif is an oral typhoid vaccine containing live, attenuated Salmonella enterica serovar Typhi strain Ty21a. It is the only licensed oral typhoid vaccine available worldwide and is used to protect adults and children aged 5 years and older against typhoid fever, a potentially life-threatening systemic infection endemic to many low- and middle-income countries. The vaccine is administered as a course of three enteric-coated capsules taken on alternate days (days 1, 3, and 5), providing protection that begins approximately 7 to 10 days after completing the series and lasts for about 3 years. Vivotif is recommended by the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and national health authorities for travelers to endemic regions, laboratory workers handling Salmonella Typhi, and individuals in close contact with chronic typhoid carriers.
Quick Facts: Vivotif
Key Takeaways
- Vivotif is the only licensed oral typhoid vaccine worldwide, containing live attenuated Salmonella Typhi Ty21a bacteria that stimulate both mucosal and systemic immune responses without causing typhoid fever.
- The vaccine is taken as three capsules on alternate days (days 1, 3, and 5) on an empty stomach with cold or lukewarm water, and protection begins approximately 7–10 days after completing the full course.
- Vivotif provides protection for approximately 3 years, after which a complete revaccination course is recommended for continued travel to endemic areas.
- The vaccine must not be taken concurrently with antibiotics or within 3 days of antibiotic treatment, and antimalarial medications should be delayed until at least 3 days after the final Vivotif dose.
- Vivotif is contraindicated in immunocompromised individuals, during acute febrile or gastrointestinal illness, and in children under 5 years of age; it should be stored refrigerated at 2–8°C.
What Is Vivotif and What Is It Used For?
Vivotif contains live bacteria of the Salmonella enterica serovar Typhi strain Ty21a, which have been genetically attenuated so they can no longer cause typhoid fever in vaccinated individuals. Despite their inability to produce disease, these attenuated organisms retain enough of the structural and antigenic properties of wild-type Salmonella Typhi to effectively stimulate the immune system. When the enteric-coated capsules are swallowed and reach the small intestine, the live bacteria colonize the intestinal mucosa and interact with the gut-associated lymphoid tissue (GALT), including Peyer's patches, triggering a comprehensive immune response.
The immune response elicited by Vivotif is multifaceted and involves both humoral and cell-mediated components. On the humoral side, the vaccine induces the production of secretory immunoglobulin A (sIgA) antibodies in the intestinal mucosa, which serve as the first line of defense against ingested Salmonella Typhi organisms. These mucosal antibodies can neutralize the bacteria before they penetrate the intestinal epithelium and enter the bloodstream. Additionally, serum IgG antibodies against Salmonella Typhi O and H antigens are produced, contributing to systemic immunity. On the cellular side, Vivotif activates CD4+ and CD8+ T lymphocytes that can recognize and destroy cells infected with Salmonella Typhi, providing an additional layer of protection against intracellular bacterial survival.
Typhoid fever is a serious systemic infection caused by the bacterium Salmonella enterica serovar Typhi, transmitted through contaminated food and water. The World Health Organization estimates that typhoid fever causes approximately 9 million cases and 110,000 deaths annually worldwide, with the highest burden in South Asia, Southeast Asia, sub-Saharan Africa, and parts of Central and South America. The disease is characterized by sustained high fever, headache, abdominal pain, and either constipation or diarrhea. Without appropriate antibiotic treatment, typhoid fever can lead to life-threatening complications including intestinal perforation, hemorrhage, encephalopathy, and multi-organ failure. The increasing emergence of multidrug-resistant and extensively drug-resistant strains of Salmonella Typhi underscores the importance of vaccination as a primary prevention strategy.
Clinical trials and post-marketing surveillance studies have demonstrated that Vivotif provides approximately 50–80% protection against typhoid fever, depending on the study population and endemic conditions. In a landmark field trial conducted in Santiago, Chile, involving over 500,000 school-age children, a three-dose regimen of Vivotif provided 67% protective efficacy over a three-year follow-up period. Similar levels of protection have been observed in field trials conducted in Indonesia and other endemic settings. While no typhoid vaccine provides 100% protection, the combination of vaccination with appropriate food and water hygiene precautions offers the most comprehensive approach to preventing typhoid fever during travel to endemic areas.
Vivotif is approved for use in adults and children aged 5 years and older. It is the preferred typhoid vaccine for many travelers because of its oral route of administration, which avoids the need for an injection. The vaccine is widely recommended by international public health authorities including the WHO, CDC, and the European Centre for Disease Prevention and Control (ECDC) for specific populations at increased risk of typhoid fever exposure.
Vivotif provides protection specifically against typhoid fever caused by Salmonella Typhi. It does not protect against paratyphoid fever (caused by Salmonella Paratyphi) or against the much more common non-typhoidal Salmonella infections that cause gastroenteritis (food poisoning). These non-typhoidal Salmonella species are caused by different bacterial serotypes with distinct antigenic properties. Always maintain food and water hygiene precautions when traveling, regardless of vaccination status.
What Should You Know Before Taking Vivotif?
Before receiving Vivotif, it is essential to discuss your complete medical history with your healthcare provider, including any current illnesses, medications, allergies, and immune system conditions. Because Vivotif is a live attenuated vaccine, there are specific contraindications and precautions that must be carefully considered to ensure both the safety and efficacy of the vaccination.
Contraindications
Vivotif must not be used in the following situations, as doing so could pose serious health risks or render the vaccine ineffective:
- Hypersensitivity: Do not take Vivotif if you have a known allergy to Salmonella Typhi Ty21a or any of the other ingredients in the vaccine, including lactose, sucrose, casein hydrolysate, ascorbic acid, magnesium stearate, gelatin, or any of the capsule shell components. If you have experienced an allergic reaction to a previous dose of Vivotif, you must not receive further doses.
- Immunodeficiency: Vivotif is contraindicated in individuals with compromised immune systems. This includes congenital (primary) immunodeficiency disorders, HIV/AIDS (particularly those with CD4 counts below 200 cells/mm³), active malignant disease, and immunosuppression caused by medications such as high-dose corticosteroids (equivalent to prednisolone ≥20 mg/day for ≥2 weeks), chemotherapy, radiation therapy, or biologic immunosuppressive agents (such as TNF inhibitors or anti-CD20 antibodies). Organ transplant recipients receiving immunosuppressive therapy should also not receive this vaccine.
- Acute illness: Do not take Vivotif during acute febrile illness (fever above 38.5°C / 101.3°F) or acute gastrointestinal illness such as diarrhea or vomiting. These conditions can impair the immune response to the vaccine and may interfere with the survival and replication of the vaccine organisms in the gut. Wait until you have fully recovered before starting the vaccination course.
Warnings and Precautions
Even when the vaccine is taken correctly and the full course is completed, not all individuals will develop complete protection against typhoid fever. The protective efficacy of Vivotif ranges from approximately 50–80%, meaning that a proportion of vaccinated individuals may still be susceptible to infection. For this reason, it is critical to continue following food and water hygiene recommendations when traveling in typhoid-endemic areas, including drinking only bottled or boiled water, avoiding ice from unknown sources, eating thoroughly cooked hot foods, and peeling fruits yourself.
Individuals receiving the vaccine should be aware that severe allergic reactions (anaphylaxis), though extremely rare, can occur with any vaccine. Symptoms of anaphylaxis include swelling of the face or throat, difficulty breathing, rapid heartbeat, dizziness, and loss of consciousness. If you experience any of these symptoms after taking a Vivotif capsule, seek immediate medical attention.
Children and Adolescents
Vivotif is not recommended for children under 5 years of age because the enteric-coated capsule is not suitable for young children who may have difficulty swallowing capsules whole. For children aged 2 years and older who require typhoid protection, the injectable Vi polysaccharide vaccine (Typhim Vi) is an alternative option. For children aged 6 months and older in highly endemic settings, the newer typhoid conjugate vaccine (TCV) is recommended by the WHO as the preferred option for routine immunization programs.
Pregnancy and Breastfeeding
The safety of Vivotif during pregnancy has not been established through controlled clinical trials. As a general principle, live vaccines are not recommended during pregnancy due to the theoretical risk to the developing fetus, even though no adverse effects have been reported with Vivotif in pregnant women. If you are pregnant, planning to become pregnant, or breastfeeding, consult your healthcare provider to weigh the benefits of vaccination against the potential risks. In situations where travel to a high-risk typhoid-endemic area cannot be avoided, the injectable Vi polysaccharide vaccine (an inactivated vaccine) may be a safer alternative during pregnancy.
It is not known whether the attenuated vaccine organisms are excreted in breast milk. However, because Vivotif is administered orally and the attenuated bacteria primarily colonize the gastrointestinal tract, the risk to a breastfed infant is considered to be low. Discuss the risks and benefits with your doctor before making a decision.
Vivotif is not expected to affect the ability to drive or use machines. However, if you experience side effects such as dizziness, fatigue, or general malaise after taking the vaccine, you should not drive or operate machinery until you feel well again. Always assess your own fitness before undertaking activities that require alertness.
Lactose and Sucrose Content
Vivotif capsules contain lactose and sucrose as excipients. If you have been diagnosed with an intolerance to certain sugars (such as lactose intolerance, fructose intolerance, glucose-galactose malabsorption, or sucrase-isomaltase insufficiency), inform your healthcare provider before taking this vaccine, as these conditions may affect tolerability.
How Does Vivotif Interact with Other Drugs?
Because Vivotif is a live bacterial vaccine, its effectiveness depends on the survival, replication, and interaction of the attenuated Salmonella Typhi Ty21a organisms with the immune system in the gut. Any medication or substance that kills or inhibits these bacteria, or that suppresses the immune response, can significantly reduce the vaccine's protective efficacy. It is therefore essential to inform your healthcare provider about all medications you are currently taking, have recently taken, or plan to take, including prescription drugs, over-the-counter medications, and herbal or traditional remedies.
Major Interactions
| Drug / Class | Interaction | Recommendation |
|---|---|---|
| Antibiotics (all classes) | Can kill the live attenuated bacteria, preventing immune response | Stop antibiotics at least 3 days before first Vivotif dose |
| Immunosuppressants | Suppress immune response; risk of disseminated infection from live vaccine | Vivotif is contraindicated; consider injectable Vi vaccine instead |
| High-dose corticosteroids | Doses ≥20 mg prednisolone/day for ≥2 weeks suppress immune function | Contraindicated; wait at least 1 month after stopping before vaccination |
| Biologic agents (TNF inhibitors, anti-CD20) | Profoundly suppress immune function; live vaccines may cause infection | Contraindicated; use inactivated typhoid vaccine alternative |
Minor Interactions
| Drug / Class | Interaction | Recommendation |
|---|---|---|
| Mefloquine (antimalarial) | May have antibacterial activity that reduces vaccine efficacy | Start mefloquine at least 3 days after last Vivotif dose |
| Proguanil (antimalarial) | Antibacterial properties may interfere with live vaccine organisms | Start proguanil at least 3 days after last Vivotif dose |
| Chloroquine (antimalarial) | Potential interference with vaccine bacteria in the gut | Start chloroquine at least 3 days after last Vivotif dose |
| Other live vaccines | Possible immune interference if given simultaneously | Can be given simultaneously or at any interval; no specific spacing required |
Vivotif can generally be administered at the same time as other routine travel vaccines, including those for hepatitis A, hepatitis B, yellow fever, rabies, Japanese encephalitis, and injectable polio vaccine. There is no evidence that co-administration with these vaccines reduces the efficacy of Vivotif or the other vaccines. However, because of the interaction with antimalarials, it is important to plan the timing of your vaccinations carefully when preparing for travel, ideally starting the Vivotif course well in advance of departure so that the three-day waiting period before starting antimalarials does not conflict with your travel schedule.
What Is the Correct Dosage of Vivotif?
Always take Vivotif exactly as directed by your healthcare provider or pharmacist. The following dosage information represents the standard recommended regimen approved by regulatory authorities worldwide. If you are unsure about any aspect of the dosing schedule, consult your healthcare provider before starting the course.
Adults and Children (5 Years and Older)
Standard Vaccination Course
The recommended dose is three capsules, taken one capsule every other day:
- Day 1: Take the first capsule
- Day 3: Take the second capsule
- Day 5: Take the third capsule
| Patient Group | Dose | Schedule | Notes |
|---|---|---|---|
| Adults (18+ years) | 1 capsule per dose | Days 1, 3, 5 (3 doses total) | Complete at least 7 days before travel |
| Children (5–17 years) | 1 capsule per dose | Days 1, 3, 5 (3 doses total) | Must be able to swallow capsules whole |
| Children (<5 years) | Not recommended | N/A | Use injectable typhoid vaccine instead |
| Revaccination | 1 capsule per dose | Days 1, 3, 5 (full 3-dose course) | Every 3 years if continued exposure |
How to Take the Capsules
Proper administration is critical for Vivotif to work effectively. Before taking each capsule, check that the blister packaging is intact and that the capsules show no signs of damage or discoloration. Follow these steps carefully:
- Take on an empty stomach: Take each capsule at least one hour before your next meal. Food in the stomach can interfere with the enteric coating and expose the live bacteria to stomach acid, potentially destroying them before they reach the small intestine.
- Swallow whole: Do not crush, chew, or open the capsules. The enteric coating is specifically designed to protect the live bacteria from stomach acid and to ensure they are released in the alkaline environment of the small intestine where they can effectively colonize and stimulate the immune system.
- Use cold or lukewarm water: Swallow each capsule with cold or lukewarm water (not exceeding 37°C / 98.6°F). Hot beverages can damage or kill the live attenuated bacteria within the capsule.
- Swallow promptly: Place the capsule in your mouth and swallow it as quickly as possible to minimize exposure to saliva and oral warmth, which could begin to dissolve the enteric coating prematurely.
Timing Before Travel
Protection against typhoid fever begins approximately 7 to 10 days after completing the full three-dose course. This means the last capsule should ideally be taken at least 7 to 10 days before arriving in a typhoid-endemic area. When planning your vaccination schedule, factor in the 5 days needed to complete the course plus the 7–10 day onset period, meaning you should ideally start the Vivotif course at least 2 to 3 weeks before your departure date.
Missed Dose
If you forget to take a capsule on the scheduled day, take it as soon as you remember. Then take the next capsule approximately 48 hours later, maintaining the alternate-day schedule. It is important to complete all three doses for adequate protection. If the interval between doses is significantly extended, consult your healthcare provider about whether to restart the course, as prolonged gaps between doses may reduce the immune response.
Overdose
If you accidentally take all three capsules at once, or if a child ingests the vaccine by mistake, contact your healthcare provider or poison control center for assessment and advice. You are unlikely to become ill from taking multiple doses simultaneously, as the vaccine contains attenuated (weakened) bacteria that cannot cause typhoid fever. However, you may not achieve adequate protection because the immune system responds best when the three doses are spaced apart as recommended, allowing the immune response to develop progressively with each dose.
After the initial three-dose course, protection against typhoid fever lasts approximately 3 years. If you continue to travel to or live in areas where typhoid fever is endemic, a complete revaccination course of three capsules (days 1, 3, and 5) is recommended every 3 years. There is no need for a booster dose between revaccination courses. Contact your healthcare provider to discuss your ongoing typhoid vaccination needs based on your travel plans and risk assessment.
What Are the Side Effects of Vivotif?
Like all vaccines, Vivotif can cause side effects, although not everyone experiences them. The overall safety profile of Vivotif is well-established through decades of clinical use and post-marketing surveillance involving millions of doses administered worldwide. Most side effects are mild, self-limiting, and resolve within 1 to 3 days without medical intervention. The gastrointestinal side effects are expected given the oral route of administration and the fact that the live attenuated bacteria interact with the intestinal immune system.
Contact emergency services immediately if you experience signs of a severe allergic reaction (anaphylaxis) after taking Vivotif. Symptoms include: swelling of the face, lips, tongue, or throat; difficulty breathing or swallowing; sudden drop in blood pressure; rapid heartbeat; dizziness or loss of consciousness; and widespread hives or skin rash. Although extremely rare with Vivotif, anaphylaxis is a medical emergency that requires immediate treatment.
Common Side Effects
May affect up to 1 in 10 people
- Abdominal pain or stomach cramps
- Nausea
- Vomiting
- Diarrhea
- Fever (pyrexia)
- Headache
- Skin redness (erythema)
Frequency Not Known
Cannot be estimated from available data
- Skin irritation, rash, urticaria (hives), and itching (pruritus)
- Weakness (asthenia)
- General malaise (feeling unwell)
- Chills
- Fatigue
- Tingling and numbness (paresthesia)
- Dizziness
- Joint pain (arthralgia) or muscle pain (myalgia)
- Back pain
- Decreased appetite, flatulence, abdominal distension
- Influenza-like illness
The gastrointestinal side effects of Vivotif are generally explained by the mechanism of action of the vaccine. The live attenuated Salmonella Typhi Ty21a bacteria colonize the intestinal mucosa and stimulate a local immune response, which can cause temporary inflammation and irritation of the gastrointestinal tract. This is a normal part of the immune response process and indicates that the vaccine is working as intended.
Systemic side effects such as fever, headache, fatigue, and muscle aches reflect the activation of the broader immune system in response to the vaccine antigens. These symptoms typically appear within 24 to 48 hours of taking a capsule and resolve spontaneously within 1 to 3 days. Over-the-counter medications such as paracetamol (acetaminophen) can be used to manage fever and pain if needed, but avoid taking non-steroidal anti-inflammatory drugs (NSAIDs) unless recommended by your healthcare provider.
Long-term side effects have not been reported with Vivotif. The live attenuated bacteria are cleared from the body within days to weeks after vaccination, and the vaccine does not establish persistent infection. Post-marketing surveillance data spanning more than three decades of global use have confirmed the excellent long-term safety profile of Vivotif.
If you experience any side effects, including any not listed above, tell your healthcare provider or pharmacist. You can also report suspected side effects directly to your national pharmacovigilance authority (e.g., the FDA MedWatch program in the United States, the Yellow Card Scheme in the United Kingdom, or the EMA EudraVigilance system in the European Union). By reporting side effects, you help provide more information on the safety of this vaccine.
How Should You Store Vivotif?
Proper storage of Vivotif is critical to maintaining the viability of the live attenuated bacteria within the capsules and ensuring the vaccine remains effective. Unlike many conventional oral medications that can be stored at room temperature, Vivotif requires continuous cold chain storage from the time of manufacture until the moment of administration.
Temperature requirements: Store Vivotif in a refrigerator at a temperature between 2°C and 8°C (36°F to 46°F). Do not freeze the vaccine, as freezing can damage both the live bacteria and the enteric coating of the capsules. If the vaccine has been frozen at any point, do not use it and dispose of it properly.
Light protection: Keep the blister packaging inside the outer cardboard carton at all times. The live bacteria in Vivotif are sensitive to light exposure, which can reduce their viability and the potency of the vaccine.
Expiry date: Do not use Vivotif after the expiry date printed on the label and carton. The expiry date refers to the last day of the stated month. After the expiry date, the number of viable bacteria may have declined below the minimum required for an effective immune response.
Packaging integrity: Before taking each capsule, inspect the blister packaging to ensure it is intact and undamaged. If the blister foil is torn or punctured, or if the capsules appear damaged, discolored, or broken, do not use the vaccine. Compromised packaging may have allowed moisture, air, or contaminants to reach the capsules, potentially reducing the viability of the live bacteria.
Disposal: Do not dispose of unused or expired vaccines in household waste or down the drain. Return unused vaccines to your pharmacy for proper disposal according to local regulations. These measures help protect the environment and prevent accidental exposure.
Keep Vivotif out of the sight and reach of children. While the attenuated bacteria cannot cause typhoid fever, accidental ingestion by a young child could cause gastrointestinal discomfort and would waste vaccine doses that may be needed for the intended recipient.
What Does Vivotif Contain?
Active Ingredient
Each enteric-coated capsule contains a minimum of 2 × 109 (2 billion) colony-forming units (CFU) of live, attenuated Salmonella enterica serovar Typhi strain Ty21a. This bacterial strain was derived from the wild-type Salmonella Typhi strain Ty2 through chemical mutagenesis, resulting in the loss of the Vi capsular polysaccharide and the galE gene function. These genetic modifications render the bacteria unable to cause typhoid fever while preserving the antigenic structures necessary to stimulate protective immunity.
Other Ingredients (Excipients)
| Component | Ingredient | Function |
|---|---|---|
| Capsule contents | Anhydrous lactose | Bulking agent and bacterial stabilizer |
| Capsule contents | Sucrose | Cryoprotectant for bacterial viability |
| Capsule contents | Casein hydrolysate | Nutrient source for bacteria |
| Capsule contents | Ascorbic acid (E300) | Antioxidant |
| Capsule contents | Magnesium stearate (E470) | Lubricant for capsule filling |
| Capsule shell | Gelatin, titanium dioxide (E171), erythrosine (E127), yellow iron oxide (E172), red iron oxide (E172) | Capsule structure and coloring |
| Enteric coating | Hypromellose phthalate, ethylene glycol, diethyl phthalate | Acid-resistant coating for gastric protection |
Appearance and Packaging
Vivotif capsules are two-toned, with a white opaque body and a salmon-pink (peach/orange) opaque cap. Each package contains one blister strip of three enteric-coated capsules, which constitutes one complete vaccination course. The capsules should be uniform in appearance with no signs of cracking, discoloration, or moisture damage. The enteric coating gives the capsules a slightly glossy finish.
The vaccine also contains non-viable (dead) cells of Salmonella Typhi Ty21a as part of the manufacturing process. These non-viable cells do not contribute to the immune response but are a natural component of the lyophilized bacterial preparation.
Frequently Asked Questions About Vivotif
Vivotif is an oral typhoid vaccine used to protect against typhoid fever caused by Salmonella Typhi. It is primarily recommended for travelers visiting regions where typhoid fever is common, including parts of South Asia, Southeast Asia, Africa, and Central and South America. The vaccine is approved for adults and children aged 5 years and older, and it is also recommended for laboratory workers handling Salmonella Typhi cultures and individuals in close contact with chronic typhoid carriers.
Vivotif is taken as three enteric-coated capsules on alternate days: one capsule on day 1, day 3, and day 5. Each capsule should be swallowed whole on an empty stomach (at least one hour before a meal) with cold or lukewarm water not exceeding 37°C. Do not crush or chew the capsules, as the enteric coating protects the live bacteria from stomach acid. Protection begins approximately 7–10 days after completing all three doses.
No, Vivotif must not be taken at the same time as antibiotics. Because Vivotif contains live bacteria, antibiotics can kill the vaccine organisms and prevent the development of an immune response. You should finish any course of antibiotics and wait at least 3 days before starting the Vivotif vaccination series. Similarly, do not start antibiotics during the 5-day vaccination period unless medically necessary, in which case you may need to repeat the entire Vivotif course after the antibiotics are completed.
Vivotif provides protection against typhoid fever for approximately 3 years. If you continue to visit or live in typhoid-endemic areas after this period, a complete revaccination course of three capsules (days 1, 3, and 5) is recommended. There is no single booster dose; the full three-dose course must be repeated. Importantly, no typhoid vaccine offers 100% protection, so food and water hygiene precautions should always be followed when traveling in endemic regions.
Vivotif is approved for children aged 5 years and older who can swallow capsules whole. It is not recommended for children under 5 years because the enteric-coated capsule form is not suitable for younger children. For younger children who need typhoid protection, the injectable Vi polysaccharide vaccine (approved for children aged 2 and older) or the newer typhoid conjugate vaccine (TCV, approved for children aged 6 months and older in some countries) are available alternatives. Consult your pediatrician or travel medicine specialist for guidance on the most appropriate option for your child.
No, Vivotif is contraindicated in individuals with compromised immune systems. Because it is a live vaccine, the attenuated bacteria could potentially cause infection in people whose immune systems cannot adequately control them. This includes individuals with HIV/AIDS (especially those with low CD4 counts), people receiving immunosuppressive therapy (including high-dose steroids, chemotherapy, biologic agents, or radiation), organ transplant recipients, and those with congenital immunodeficiency disorders. For immunocompromised individuals who need typhoid protection, the injectable Vi polysaccharide vaccine (an inactivated vaccine) is a safer alternative.
References
- World Health Organization. Typhoid vaccines: WHO position paper – March 2018. Weekly Epidemiological Record. 2018;93(13):153–172.
- European Medicines Agency. Vivotif – Summary of Product Characteristics. Last updated October 2023.
- Centers for Disease Control and Prevention. CDC Yellow Book 2024: Health Information for International Travel – Typhoid & Paratyphoid Fever. Oxford University Press; 2024.
- Advisory Committee on Immunization Practices (ACIP). Prevention of Typhoid Fever – Updated Recommendations. MMWR Recommendations and Reports. 2020.
- Levine MM, Ferreccio C, Abrego P, et al. Duration of efficacy of Ty21a, attenuated Salmonella Typhi live oral vaccine. Vaccine. 1999;17(Suppl 2):S22–S27.
- Black RE, Levine MM, Ferreccio C, et al. Efficacy of one or two doses of Ty21a Salmonella Typhi vaccine in enteric-coated capsules in a controlled field trial. Vaccine. 1990;8(1):81–84.
- British National Formulary (BNF). Typhoid vaccine, live (oral) – Vivotif. National Institute for Health and Care Excellence (NICE). Updated 2025.
- Anwar E, Goldberg E, Fraser A, et al. Vaccines for preventing typhoid fever. Cochrane Database of Systematic Reviews. 2014;(1):CD001261.
- Milligan R, Paul M, Richardson M, Neuberger A. Vaccines for preventing typhoid fever. Cochrane Database of Systematic Reviews. 2018;(5):CD001261.
- European Centre for Disease Prevention and Control (ECDC). Typhoid fever – Annual epidemiological report. ECDC; 2024.
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