Typhoid Vaccines
Introduction to Typhoid Vaccines
Typhoid vaccines are immunizations designed to protect against Salmonella enterica serovar Typhi, the causative agent of typhoid fever. These vaccines have been crucial in reducing the global burden of typhoid, particularly in endemic regions.
Key points:
- First typhoid vaccine developed in 1896 by Almroth Wright
- Modern vaccines include live attenuated, inactivated whole-cell, and subunit vaccines
- Recommended for travelers to endemic areas and for population-wide use in high-risk regions
- Ongoing research focuses on improving vaccine efficacy and developing combination vaccines
Salmonella Typhi and Typhoid Fever
Salmonella enterica serovar Typhi
- Gram-negative, rod-shaped bacterium
- Obligate human pathogen with no known animal reservoir
- Transmitted through contaminated food and water
Typhoid Fever
- Systemic illness characterized by fever, abdominal pain, and general malaise
- Incubation period: 7-14 days
- Can lead to severe complications if untreated (e.g., intestinal perforation, sepsis)
- Global burden: Estimated 11-20 million cases and 128,000-161,000 deaths annually
Antibiotic Resistance
Increasing antibiotic resistance, including multidrug-resistant and extensively drug-resistant strains, underscores the importance of prevention through vaccination.
Types of Typhoid Vaccines
Several types of typhoid vaccines are currently available or in development:
1. Live Attenuated Oral Vaccine (Ty21a)
- Contains live attenuated S. Typhi strain Ty21a
- Administered orally in 3-4 doses
- Provides both humoral and cell-mediated immunity
- Brand name: Vivotif
2. Vi Capsular Polysaccharide Vaccine
- Purified Vi antigen from the bacterial capsule
- Single intramuscular injection
- Induces primarily humoral immunity
- Brand names: Typhim Vi, Typherix
3. Typhoid Conjugate Vaccine (TCV)
- Vi antigen conjugated to a carrier protein (e.g., tetanus toxoid)
- Single intramuscular injection
- Induces stronger, longer-lasting immunity than Vi polysaccharide vaccine
- Suitable for use in young children
- Brand name: Typbar-TCV
4. Inactivated Whole-Cell Vaccine
- Historical vaccine, largely replaced by newer formulations
- No longer recommended due to high reactogenicity
Efficacy and Safety of Typhoid Vaccines
Efficacy
- Ty21a: 51-67% effective over 3 years
- Vi polysaccharide: 55-72% effective over 3 years
- Typhoid conjugate vaccine (TCV): 81-85% effective over at least 2 years
Safety Profile
- Ty21a: Generally well-tolerated; rare gastrointestinal side effects
- Vi polysaccharide: Mild local reactions; rarely, fever or headache
- TCV: Similar safety profile to Vi polysaccharide; well-tolerated in children
Duration of Protection
Protection wanes over time, necessitating boosters:
- Ty21a: Boosters recommended every 5 years
- Vi polysaccharide: Boosters recommended every 2-3 years
- TCV: Longer-lasting protection, exact duration still under study
Typhoid Vaccination Schedule
Vaccination schedules vary by vaccine type and local recommendations:
Ty21a Oral Vaccine
- 4 doses given on alternate days (days 1, 3, 5, and 7)
- Recommended for individuals ≥6 years old
- Booster every 5 years if continued exposure or travel
Vi Capsular Polysaccharide Vaccine
- Single intramuscular dose
- Recommended for individuals ≥2 years old
- Booster every 2-3 years if continued exposure or travel
Typhoid Conjugate Vaccine (TCV)
- Single intramuscular dose
- Can be given to children as young as 6 months
- Booster recommendations still under study
Timing with Other Vaccines
Typhoid vaccines can generally be administered concurrently with other vaccines, using separate syringes and injection sites for parenteral vaccines.
Contraindications and Precautions
Contraindications
- Severe allergic reaction to a previous dose or vaccine component
- Ty21a: Immunocompromised individuals, active gastrointestinal illness
Precautions
- Moderate or severe acute illness
- Pregnancy (benefit should outweigh risk)
- Ty21a: Recent antibiotic use may reduce vaccine efficacy
Special Considerations
Vi polysaccharide and TCV are preferred for individuals with HIV infection. Ty21a should not be given to individuals taking antibiotics; administration should be delayed until 3 days after antibiotic completion.
Typhoid Vaccination in Special Populations
Travelers
- Recommended for travelers to endemic areas, especially South Asia
- Should be completed at least 1-2 weeks before travel
Children
- TCV is preferred due to its efficacy in young children
- Vi polysaccharide can be used in children ≥2 years
- Ty21a is licensed for children ≥6 years in most countries
Immunocompromised Individuals
- Vi polysaccharide or TCV recommended
- Ty21a contraindicated due to theoretical risk of invasive infection
Healthcare Workers
Vaccination may be considered for laboratory workers regularly exposed to S. Typhi.
Global Impact of Typhoid Vaccination
Typhoid vaccination has had significant public health benefits, particularly in endemic regions:
- Reduction in typhoid fever incidence and associated mortality
- Decreased economic burden due to reduced healthcare costs and lost productivity
- Potential to combat antibiotic resistance by reducing overall disease burden
Challenges and Considerations
- Limited vaccine coverage in many endemic areas
- Need for improved vaccines with longer duration of protection
- Integration with water, sanitation, and hygiene (WASH) interventions
- Cost-effectiveness and feasibility of large-scale vaccination programs
WHO Recommendations
The World Health Organization recommends the programmatic use of typhoid vaccines for control of endemic and epidemic typhoid fever, with a preference for TCV due to its improved immunogenicity and potential for use in younger children.
Future Directions in Typhoid Vaccination
Research and Development
- Improved conjugate vaccines with broader coverage and longer-lasting immunity
- Development of combination vaccines (e.g., typhoid-paratyphoid)
- Novel delivery methods to enhance mucosal immunity
Implementation Strategies
- Integration of typhoid vaccination into routine immunization programs
- Targeted vaccination campaigns in high-risk areas
- Improved surveillance and monitoring of vaccine impact
One Health Approach
Future strategies may incorporate a One Health approach, addressing human, animal, and environmental factors contributing to typhoid transmission and antimicrobial resistance.
Typhoid Vaccines
- What causes typhoid fever?
Salmonella Typhi bacteria - How is typhoid typically transmitted?
Through contaminated food and water - What are the two main types of typhoid vaccines?
Oral live attenuated vaccine and injectable inactivated vaccine - How long does protection from the oral typhoid vaccine last?
Approximately 5 years - How long does protection from the injectable typhoid vaccine last?
Approximately 2-3 years - At what age can the oral typhoid vaccine be given?
6 years and older - Can pregnant women receive the typhoid vaccine?
Injectable vaccine is preferred; oral vaccine is not recommended - How many doses are required for the oral typhoid vaccine?
4 doses taken every other day - How many doses are required for the injectable typhoid vaccine?
Single dose - What is the efficacy of the typhoid vaccine?
50-80%, depending on the type of vaccine - Can the typhoid vaccine prevent all cases of typhoid fever?
No, it reduces the risk but doesn't provide 100% protection - Who should consider getting the typhoid vaccine?
Travelers to areas where typhoid is common and people in close contact with typhoid carriers - What are common side effects of the oral typhoid vaccine?
Stomach pain, nausea, fever, and headache - What are common side effects of the injectable typhoid vaccine?
Pain and redness at the injection site, fever - Can the typhoid vaccine be given with other travel vaccines?
Yes, it can be administered with other vaccines - How soon before travel should the typhoid vaccine be given?
At least 2 weeks before travel for full protection - Is the typhoid vaccine part of routine childhood immunizations in most countries?
No, it's primarily recommended for travelers and high-risk groups - Can someone who has had typhoid fever still benefit from the vaccine?
Yes, as past infection doesn't confer lifelong immunity - What is the name of the oral typhoid vaccine?
Vivotif (Ty21a) - What is the name of the injectable typhoid vaccine?
Typhim Vi - Can immunocompromised individuals receive the oral typhoid vaccine?
No, they should receive the injectable vaccine - How should the oral typhoid vaccine be stored?
Refrigerated (2°C to 8°C) - Can antibiotics affect the efficacy of the oral typhoid vaccine?
Yes, antibiotics should be avoided for 7 days before and after vaccination - Is there a combination vaccine that includes typhoid protection?
Yes, a combined hepatitis A and typhoid vaccine is available in some countries - Can the typhoid vaccine cause typhoid fever?
No, neither the oral nor injectable vaccine can cause typhoid fever - In which year was the first typhoid vaccine developed?
1896 - Which organization recommends typhoid vaccination for global use?
The World Health Organization (WHO) - Is typhoid vaccine 100% effective in preventing infection?
No, it reduces the risk but doesn't provide complete protection - How long after vaccination does it take to develop immunity against typhoid?
About 1-2 weeks - Can children receive the typhoid vaccine?
Yes, but age restrictions vary by vaccine type
