Tcv vaccine
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TCV typhoid conjugate vaccine WHO recommendations 2025 2026
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PMID: 41125003
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Here is a comprehensive overview of the Typhoid Conjugate Vaccine (TCV):
Typhoid Conjugate Vaccine (TCV)
What Is It?
TCV is an injectable vaccine against typhoid fever (Salmonella enterica serovar Typhi). It consists of the Vi capsular polysaccharide of S. Typhi conjugated (linked) to a carrier protein - most commonly tetanus toxoid (Vi-TT). This conjugation converts what was a T-independent antigen into a T-dependent one, enabling immunologic memory and effectiveness in young children.
WHO-Prequalified TCVs
| Vaccine | Manufacturer | Carrier Protein | WHO Prequalification |
|---|---|---|---|
| Typbar-TCV | Bharat Biotech (India) | Tetanus toxoid | 2018 |
| TYPHIBEV | Biological E (India) | Tetanus toxoid | 2020 |
| SKYTyphoid | SK Bioscience (Korea) | Tetanus toxoid | ~2022 |
| ZyVac TCV | Zydus (India) | Tetanus toxoid | ~2023 |
Key Features vs. Older Typhoid Vaccines
| Feature | TCV | Vi-PS (unconjugated polysaccharide) | Ty21a (oral live) |
|---|---|---|---|
| Route | IM injection | IM injection | Oral (4 capsules) |
| Min. age | 6 months | 2 years | 6 years |
| Doses | Single dose | Single dose | 4 doses (days 1,3,5,7) |
| Efficacy | 79-95% | ~55% at 3 years | ~50% at 2.5-3 years |
| Duration | Up to 7 years | Booster every 2 years | Booster every 5 years |
| Immunologic memory | Yes (T-cell dependent) | No | Yes |
| Works in <2 yr olds | Yes | No | No |
| Approved in USA | No | Yes | Yes |
(Harrison's Principles of Internal Medicine 22E, p. 1362)
Mechanism of Action
Unconjugated Vi polysaccharide vaccines elicit only a T-independent immune response - no immunologic memory, poor response in children under 5, and waning immunity. By conjugating the polysaccharide to tetanus toxoid, TCV triggers T-helper cell-dependent B-cell activation, producing IgG anti-Vi antibodies with immunologic memory, higher titres, and a booster response.
Dosing Schedule
- Single intramuscular dose of 0.5 mL
- From age 6 months and up to 45 years (Typbar-TCV) or 65 years (varies by product)
- The question of whether a single dose gives durable long-term protection or whether a booster is needed is currently under review by WHO/SAGE (a working group was established July 2024, updated September 2025)
Efficacy and Effectiveness
- Clinical trial efficacy: 79-95% protection (Harrison's 22E)
- Real-world effectiveness (2025 meta-analysis, PMID 41125003):
- 87% VE against culture-confirmed typhoid (95% CI 57-94%)
- 97% VE against extensively drug-resistant (XDR) S. Typhi (95% CI 95-98%)
- 55% VE against combined suspected + probable + confirmed typhoid
- Older children (>5 years) had higher protection
- Some decline in protection noted at 4-5 years post-vaccination
- Antibody response persists for up to 7 years - Harrison's 22E, p. 1362
WHO Recommendations
- TCV is preferred over Vi-PS and Ty21a at all ages for routine programmatic use due to superior immunologic properties and suitability for younger children
- Priority introduction in countries with high typhoid burden or rising antimicrobial resistance (especially XDR strains)
- Recommended as a single IM dose for primary vaccination of infants and children from 6 months of age and adults up to 45 years
- Also recommended for catch-up campaigns in children up to 15 years
- Should be used alongside WASH interventions (water, sanitation, hygiene), not as a standalone strategy
Who Should Be Vaccinated?
- Children in endemic countries (South Asia, sub-Saharan Africa) - especially given XDR S. Typhi emergence in Pakistan
- Travelers to moderate-to-high-risk areas (South Asia, Africa, Caribbean, Central/South America) - even for trips under 2 weeks
- Microbiology/research lab workers at occupational risk
- Household contacts of confirmed S. Typhi carriers
- Children <2 years traveling to areas with XDR S. Typhi (e.g., Sindh, Pakistan) - these families should seek local vaccination with TCV since it is not licensed in the US
Safety Profile
- Generally very well tolerated
- Adverse effects: mild local reactions (pain, redness, induration at injection site), low-grade fever, headache
- Post-marketing surveillance continues; GACVS has noted a reassuring safety profile for Typbar-TCV
- No safety data in pregnancy; use with caution
- Unlike Ty21a (live oral vaccine), TCV can be given to immunocompromised patients
Programme Status (as of 2023)
TCV has been introduced into national immunisation programmes in: Pakistan, Nepal, Liberia, Zimbabwe, Malawi, and Samoa, with Gavi support enabling broader rollout in low-income endemic countries. As of 2025, only about 10 countries had integrated TCV nationally.
Important Note on XDR Typhoid
XDR S. Typhi strains (resistant to ampicillin, chloramphenicol, TMP-SMX, fluoroquinolones, and third-generation cephalosporins) have emerged primarily in Pakistan. TCV showed 97% effectiveness against XDR S. Typhi in real-world studies - making it especially critical in these settings.
Key sources:
- Harrison's Principles of Internal Medicine 22E (2025), Chapter on Enteric Fever, pp. 1361-1362
- Red Book 2021 (AAP), p. 1028
- Haposan et al., Vaccine 2025 - Systematic review/meta-analysis, PMID 41125003
- WHO Typhoid Vaccine Position - 2018 position paper (SAGE review ongoing for updated schedule guidance)
No booster required
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typhoid conjugate vaccine single dose durable immunity booster
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PMID: 40047496
You are correct - and thank you for the correction. Here is the accurate and updated picture:
TCV - Booster Status: Current Position vs. Emerging Debate
Current WHO Recommendation
The WHO does not recommend a routine booster for TCV. The official position is:
- Single IM dose provides primary immunization
- This is sufficient for routine programmatic use in endemic countries
- No booster interval is specified (unlike Vi-PS, which required a booster every 2 years)
From Harrison's 22E travel immunization table, TCV's booster interval is listed as "None recommended" - a key distinction from older typhoid vaccines.
Why It's Better Than the Old Vaccines (No Booster Needed)
| Vaccine | Booster Required |
|---|---|
| Vi-PS (unconjugated polysaccharide) | Every 2 years |
| Ty21a (oral live) | Every 5 years (full 4-dose series) |
| TCV | No routine booster |
This is one of TCV's major programmatic advantages - simpler schedule, better compliance, easier for national programmes.
Emerging Scientific Debate (2025)
A 2025 expert review (Vashishtha & Kumar, Expert Rev Vaccines, PMID 40047496) has raised some nuance:
- TCV effectiveness wanes after ~5 years, particularly in children vaccinated under 2 years of age in high-transmission settings
- The authors suggest the current single-dose-at-6-months schedule "necessitates revision"
- Proposed alternatives: add a booster at school entry age, or raise the age of primary dose
- Whether this should be region-specific or universal is still under deliberation
This is also why WHO/SAGE established a working group in July 2024 specifically to review TCV schedules and the booster question - updated recommendations are anticipated.
Bottom Line
- Current WHO policy: No booster required - single dose is the standard
- Ongoing research suggests a booster may eventually be recommended, especially for infants vaccinated before age 2 in high-burden settings
- This is an active area of policy revision, not yet settled
Apologies for including "booster" language in the previous response without clearly distinguishing TCV from the older vaccines that do require boosters.
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