Ty21a

Ty21a is a live attenuated bacterial vaccine that protects against typhoid. 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 mutated chemically so as to render it harmless but nevertheless immunogenic. It is one of the three typhoid vaccines currently recommended by the World Health Organization (the other two being the Typhoid Conjugate Vaccine (TCV) and Vi capsular polysaccharide vaccine).[1]

Ty21a
Vaccine description
Target diseaseTyphoid
TypeLive bacteria
Clinical data
Trade namesVivotif
Pregnancy
category
  • US: B (No risk in non-human studies)
    Routes of
    administration    		Oral
    ATC code
    Legal status
    Legal status
    • AU: S4 (Prescription only)
    • CA: Unscheduled
    • UK: POM (Prescription only)
    • US: ℞-only
      (verify)

    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.[2]

    Medical uses

    The vaccine offers a statistically significant protection for the first seven years.[3] 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.[2]

    The Vi polysaccharide vaccine is also effective at preventing typhoid fever.[3]

    Dosing

    The recommended dose varies according to country and preparation. At least three doses are required for protection.[4]

    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.[5]

    Side effects

    Side effects of this vaccine are mild and rare.[3][4]

    Trade names
    • Vivotif (manufactured by PaxVax)

    Research

    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.[3]

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    References
    1. "WHO position paper on typhoid Vaccines, March 2018" (PDF). World Health Organization. March 2018. Retrieved 2019-05-05.
    2. World Health Organization (February 2008). "Typhoid vaccines: WHO position paper" (PDF). Releve Epidemiologique Hebdomadaire. 83 (6): 49–59. PMID 18260212.
    3. Milligan, Rachael; Paul, Mical; Richardson, Marty; Neuberger, Ami (31 May 2018). "Vaccines for preventing typhoid fever". The Cochrane Database of Systematic Reviews. 5: CD001261. doi:10.1002/14651858.CD001261.pub4. ISSN 1469-493X. PMC 6494485. PMID 29851031.
    4. "World Health Organization Information sheet: Observed rate of vaccine reactions- Typhoid Vaccine" (PDF). WHO. April 2014.
    5. Salisbury D, Ramsay M, Noakes K (2006-12-11). ""Chapter 33: Typhoid"" (PDF). Immunisation against infectious disease. Department of Health. p. 418. ISBN 0-11-322528-8.
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