1. Basic Information
Disease Overview
- Typhoid Fever: Systemic infection caused by Salmonella enterica serovar Typhi, transmitted via contaminated food and water. Causes prolonged high fever, abdominal pain, and can lead to intestinal perforation or death. Case-fatality is 10–20% untreated, <1% with prompt antibiotics. WHO estimates ~9 million cases and ~110,000 deaths annually, concentrated in South Asia and sub-Saharan Africa.
- Antimicrobial resistance: Extensively drug-resistant (XDR) typhoid strains, first identified in Pakistan in 2016, have accelerated vaccine introduction in some endemic countries.
Vaccine Options
| Vaccine | Type | Schedule | Booster |
|---|---|---|---|
| ViCPS (Typhim Vi) | Injectable Vi capsular polysaccharide | Single IM dose, ≥2 years old | Every 2 years if continued exposure |
| Ty21a (Vivotif) | Oral live-attenuated | 4 capsules over 1 week, ≥6 years old | Every 5 years |
| TCV (e.g. Typbar-TCV) | Vi polysaccharide conjugated to protein carrier | Single IM dose, usable from 6 months of age; used in endemic-country programs (e.g. Pakistan EPI, Gavi-supported campaigns) | Not yet established; not licensed for routine use in the U.S. |
Source: CDC Yellow Book; WHO Typhoid position paper (2018).
Recommended For
- Travelers to regions with endemic or epidemic typhoid, especially South Asia, and those visiting friends/relatives with prolonged rural/local-food exposure.
- Laboratory workers who routinely handle S. Typhi.
- In endemic countries, TCV is increasingly offered as part of routine national infant/childhood immunization programs.
2. Pre-Licensure Clinical Trial Data
Efficacy has been evaluated in large field trials conducted primarily in endemic settings (Nepal, Bangladesh, South Africa) rather than U.S. pre-licensure trials.
| Vaccine | Efficacy Data | Evidence Strength |
|---|---|---|
| ViCPS | ~50–80% efficacy over 2–3 years across field trials (Nepal, South Africa) | Moderate |
| Ty21a | ~50–80% efficacy with full 4-dose oral course over multiple years, though real-world adherence to the full oral course is a limiting factor | Moderate |
| TCV (Typbar-TCV) | ~79–85% efficacy in a randomized controlled human challenge trial and in a large cluster-randomized field trial in Nepal; longer duration and usable in infants, an advantage over older vaccines | Strong |
Key Limitations
- Ty21a is a live vaccine: Contraindicated in immunocompromised individuals; requires refrigeration and completion of all 4 doses, which can reduce real-world effectiveness versus trial conditions.
- ViCPS does not protect young children well: Polysaccharide (non-conjugate) vaccines are poorly immunogenic in children <2 years, which is part of why TCV (a conjugate vaccine) was developed for infant use.
- TCV real-world U.S. data are sparse: Most TCV effectiveness evidence comes from South Asian and sub-Saharan African immunization programs, not U.S. travelers.
3. Post-Licensure Safety Data
Post-Licensure Safety Monitoring
Both older vaccines have decades of post-marketing use. TCV has been monitored through Gavi-supported introduction campaigns and WHO-coordinated pharmacovigilance in Pakistan, Nepal, Zimbabwe, and Liberia.
| Vaccine | Key Post-Licensure Finding |
|---|---|
| ViCPS | No unusual safety signals identified over decades of use; injection site and mild systemic reactions are the dominant reported events |
| Ty21a | Well tolerated; GI symptoms are the main reported events; rare reports of urticaria/rash |
| TCV | Large-scale campaign pharmacovigilance in Pakistan (>10 million doses) and Nepal field trial found no unexpected serious adverse event signal |
⚠ Critical Caveat
No typhoid vaccine is 100% effective and none protects against paratyphoid fever (caused by Salmonella Paratyphi); safe food and water practices remain necessary for travelers even after vaccination.
4. Documented Adverse Events — Evidence of Association
▶ Strong Evidence of Causal Association
- Injection site pain/redness (ViCPS, TCV): Common, ~10–20%. Self-limited. Strong
- Fever/headache (ViCPS, TCV): ~1–5%. Self-limited. Strong
- GI upset, nausea, abdominal discomfort (Ty21a, oral live vaccine): ~1–5%. Self-limited. Strong
▶ Moderate or Preliminary Evidence
- Urticaria/rash (Ty21a): Rare, isolated case reports; not consistently replicated across large series. Limited
5. Disease Prevention Benefits
Program Impact
| Setting | Outcome |
|---|---|
| Pakistan TCV introduction (2019–present) | Rolled out amid XDR typhoid outbreak; large-scale campaigns and routine EPI introduction associated with substantial declines in pediatric typhoid incidence in vaccinated districts |
| Nepal cluster-randomized trial (2018) | ~79% efficacy against blood-culture-confirmed typhoid over 2 years of follow-up |
| Traveler use (ViCPS/Ty21a) | Reduces but does not eliminate risk; typhoid remains one of the most common vaccine-preventable causes of fever in travelers returning from South Asia |
Source: WHO SAGE typhoid position paper (2018); Nepal TyVAC trial (Lancet, 2021 follow-up).
6. Evidence Summary
Typhoid vaccines provide moderate, time-limited protection; the newer conjugate vaccine (TCV) offers the strongest and longest-lasting efficacy data and is increasingly the preferred option in endemic-country programs. For U.S. travelers, ViCPS and Ty21a remain the standard options, each requiring periodic revaccination for continued protection. All formulations are well tolerated with adverse events limited mainly to mild, self-resolving local and systemic reactions.
| Domain | Evidence Grade | Key Finding |
|---|---|---|
| ViCPS/Ty21a efficacy | Moderate | ~50–80% over 2–5 years depending on vaccine |
| TCV efficacy | Strong | ~79–85%, usable in infants, longer duration |
| Common reactogenicity | Strong | Mild, self-limited local/systemic reactions |
| Serious adverse events | No Association | No unusual safety signal identified across decades/large campaigns |
7. Key References
- WHO. Typhoid vaccines: WHO position paper. Wkly Epidemiol Rec. 2018;93(13):153–172.
- CDC. Typhoid Fever & Paratyphoid Fever. CDC Yellow Book, Travelers’ Health. cdc.gov/yellowbook
- Meiring JE, et al. Typhoid conjugate vaccine effectiveness (TyVAC Nepal). Lancet. 2023 follow-up analyses.
- Shakya M, et al. Phase 3 efficacy analysis of a typhoid conjugate vaccine trial in Nepal. N Engl J Med. 2019;381:2209–2218.
- Gavi. Typhoid Conjugate Vaccine Support. gavi.org