Typhoid vaccine

A vaccine that reduces the risk of typhoid fever, an infection caused by Salmonella enterica serovar Typhi. Available vaccines use live attenuated bacteria or purified bacterial antigens.

Vi capsular polysaccharide: A surface polysaccharide that helps Salmonella Typhi evade immune defenses and is used in several typhoid vaccines. Vi-based vaccines train immunity against this prominent surface antigen.
Typhoid conjugate vaccine: A typhoid vaccine that couples Vi polysaccharide to a carrier protein, enabling use in young children and longer-lasting protection. It is the preferred option in many settings where available.
Typhoid conjugate vaccine versus Vi polysaccharide vaccine: A comparison of protein-conjugated and unconjugated Vi vaccines for typhoid prevention. Conjugation improves immune responses in young children and can extend protection.
Herd immunity: Indirect protection against an infectious disease that arises when enough people in a population are immune. High vaccine coverage can reduce transmission and protect people not yet vaccinated.
Vaccine efficacy: The reduction in disease among vaccinated people under controlled study conditions compared with an unvaccinated group. Trials estimate how much each typhoid vaccine reduces disease risk.
Live attenuated vaccine: A vaccine made from a weakened microorganism that can replicate but does not normally cause disease in healthy recipients. The oral Ty21a vaccine protects by presenting weakened Salmonella Typhi.
Ty21a vaccine: An oral vaccine containing live attenuated Salmonella Typhi strain Ty21a. It offers a needle-free option for eligible travelers and residents.
Oral vaccine: A vaccine administered by mouth rather than by injection. Ty21a is taken orally, unlike injectable Vi-based vaccines.
Typhoid conjugate vaccine campaign in Malawi: A 2018 vaccination campaign in Malawi that introduced typhoid conjugate vaccine to children in affected districts. The campaign provides a documented example of vaccine introduction in a high-burden setting.
Vaccine effectiveness: The reduction in disease associated with vaccination under routine real-world conditions. Field studies test whether trial protection holds across populations and settings.

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Mary MallonCompared with: Vaccination offers prevention without isolating healthy carriers.