Unlike many other diseases prevalent in low- and middle-income countries, typhoid is preventable. Typhoid vaccines offer both individual protection and herd immunity to unvaccinated individuals when used as part of a large-scale vaccination effort. Given that fundamental prevention strategies like good hygienic practices and access to clean water may be out of reach for many countries in the short-term, there is an even greater need to increase access to high-impact and cost-effective typhoid vaccines right now.
Current available vaccines include:
| Ty21a | Vi Polysaccharide | Vi Conjugate (Vi-TT) | Vi Conjugate (Vi-REPA) | |
|---|---|---|---|---|
| Availability | Private /Traveler's Market*; Limited access in developing countries | Private/Traveler's Market | Private Market-India | Private Market* |
| Type | Live Attenuated | Subunit | Subunit | Subunit |
| Route of Administration | Oral (capsular) | IM/SC (injectable) | IM/SC (injectable) | IM/SC (injectable) |
| Doses/Regimen | 4 doses (USA) | 1 dose | 1 dose | 2-3 doses |
| Revaccination | 5-7 years | 3 years | not currently recommended | not currently recommended |
| Efficacy | 35-67% | 55-72% | 92-99% | 89%+ |
| Duration of Efficacy | 62% at 7 years | 55% at 3 years | 92%+ at 2 years-life | 89%+ at 4 years-life |
| Herd Protection | Yes | Yes | Likely | Likely |
| Crossprotection Against Paratyphoid | Yes | No | No | No |
| Age | ≥6 years (USA) | ≥ 2 years (WHO; USA) | ≥6 weeks | 2-5 years |
| *Notes | Vaccine sold to PaxVax; in the process of manufacturing | Technology has been transferred to Chinese manufacturer; will be available soon in China and some developing country markets. |
Vaccination Challenges
Access: Typhoid vaccines have primarily been targeted for use in the private or traveler’s markets and have not been widely supported for use at the country level. This means that the most vulnerable populations, such as infants and young children, do not have access to the vaccine.
Effectiveness: Existing Vi polysaccharide vaccines are not effective in young children (under age two) and only provide a moderate duration of protection (two to three years) before re-vaccination is required. The cost per dose is also too high to be feasible for vulnerable communities.
The Future: Typhoid Conjugate Vaccine
Conjugate vaccines, which offer a long duration of protection and can be used in infants starting at six months of age, present a new hope in the battle against typhoid. These vaccines are highly cost effective and can be administered through the routine immunization programs in typhoid endemic countries and through programs targeting at-risk populations, such as migrants.
With the recent national licensure of a typhoid conjugate vaccine in India, and several other conjugate vaccines in the development pipeline, the roll out of a conjugate vaccine in endemic countries is now within reach.
