Ty21a is a live attenuated bacterial vaccine that protects against

typhoid Typhoid fever, also known as typhoid, is a disease caused by ''Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over several d ...

. First licensed in Europe in 1983 and in the United States in 1989, it is an orally administered, live-attenuated Ty2 strain of S. Typhi in which multiple genes, including the genes responsible for the production of Vi, have been deleted so as to render it harmless but nevertheless

immunogenic Immunogenicity is the ability of a foreign substance, such as an antigen, to provoke an immune response in the body of a human or other animal. It may be wanted or unwanted: * Wanted immunogenicity typically relates to vaccines, where the injectio ...

. It is one of the three

typhoid vaccine Typhoid vaccines are vaccines that prevent typhoid fever. Several types are widely available: typhoid conjugate vaccine (TCV), Ty21a (a live oral vaccine) and Vi capsular polysaccharide vaccine (ViPS) (an injectable subunit vaccine). They are ab ...

s currently recommended by the

World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...

(the other two being the Typhoid Conjugate Vaccine (TCV) and

Vi capsular polysaccharide vaccine The Vi capsular polysaccharide vaccine (or ViCPS) is a typhoid vaccine recommended by the World Health Organization for the prevention of typhoid (another is Ty21a). The vaccine was first licensed in the US in 1994 and is made from the purified Vi ...

). The vaccine is given by mouth. The vaccine is presented either as enteric coated capsules or as a liquid suspension. The vaccine must be stored at 2 to 8 °C, but will retain its potency for 14 days at 25 °C.

Medical uses

The vaccine offers a statistically significant protection for the first seven years. The vaccine is most commonly used to protect travelers to endemic countries, but some agencies claim that the vaccine could be used in large scale public prevention programs. The Vi polysaccharide vaccine is also effective at preventing typhoid fever.

Dosing

The recommended dose varies according to country and preparation. At least three doses are required for protection. In the US and Canada, an initial course of 4 doses on alternate days is recommended. Full protection is achieved 7 days after the last dose. In the US, a booster dose is recommended after 5 years. In Canada, a booster dose is recommended after 7 years. In Australia and Europe, an initial course of 3 doses on alternate days is recommended. Protection is achieved 7 days after the last dose. A booster dose is recommended every 3 years for people living in endemic areas, but every year for people traveling from non-endemic to endemic areas.

Side effects

Side effects of this vaccine are mild and rare.

Trade names

* Vivotif (manufactured by PaxVax)

Research

Ty21a may also provide some degree of protection against

paratyphoid fever Paratyphoid fever, also known simply as paratyphoid, is a bacterial infection caused by one of the three types of '' Salmonella enterica''. Symptoms usually begin 6–30 days after exposure and are the same as those of typhoid fever. Often, a g ...

A and B. This cross-protection by a typhoid vaccine is most likely due to

O antigen Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer ...

s shared between different ''S. enterica'' serotypes. A newer Vi-rEPA vaccine is being tested for preventing typhoid fever. It has a similar level of protection, but the protection may last longer with this newer vaccine.

References

External links

Manufacturer's Product Page
Vaccines Live vaccines Enterobacteria Typhoid fever {{Vaccine-stub