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Ty21a is a live attenuated bacterial vaccine that protects against typhoid. It is one of two typhoid vaccines currently recommended by the World Health Organization. The vaccine offers a statistically significant protection for the first three years, with between 8% to 54% effectiveness for the first year and between 40% to 71% for the second year. The vaccine is most commonly used to protect travellers to endemic countries, but there is no reason why the vaccine could not be used in large scale public prevention programmes.
The vaccine is given by mouth. The vaccine is presented either as capsules or a liquid suspension. The vaccine must be stored at 2 to 8 °C, but will retain its potency for 14 days at 25°C.
The recommended dose varies according to country.
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 is recommended every 3 years for people living in endemic areas, but every year for people travelling from non-endemic to endemic areas.
- World Health Organization (2008). "Typhoid vaccines: WHO position paper". Weekly Epidemiological Record 83 (6): 49–60. PMID 18260212.
- Fraser A, Goldberg E, Acosta CJ, Paul M, Leibovici L (2007). "Vaccines for preventing typhoid fever". In Fraser, Abigail. Cochrane Database Syst Rev (3): CD001261. doi:10.1002/14651858.CD001261.pub2. PMID 17636661.
- Salisbury, D; Ramsay, M; Noakes, K. ""Chapter 33: Typhoid"". Immunisation against infectious disease. Department of Health. p. 418. ISBN 0-11-322528-8.