Typhoid vaccines are vaccines that prevent typhoid fever. There are two types that are widely available: Ty21a (a live vaccine given by mouth) and Vi capsular polysaccharide vaccine (an injectable subunit vaccine). They are about 30 to 70% effective for the first two years depending on the specific vaccine in question.
The World Health Organization (WHO) recommends vaccinating all children in areas where the disease is common. Otherwise they recommend vaccinating those at high risk. Vaccination campaigns can also be used to control outbreaks of disease. Depending on the vaccine, additional doses are recommended every 3 to 7 years. In the United States the vaccine is only recommended in those at high risk such as travellers to areas of the world where the disease is common.
The current vaccines are very safe. Minor side effects may occur at the site of injection. The injectable vaccine is safe in HIV/AIDS and the oral vaccine can be used as long as symptoms are not present. Safety of the oral vaccine during pregnancy is unclear.
The first typhoid vaccines were developed in 1896 by Almroth Edward Wright, Richard Pfeiffer, and Wilhelm Kolle. Due to side-effects newer formulations are currently recommended. Typhoid vaccines are on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about 4.44 USD per dose as of 2014. In the United States they cost 25 to 50 USD.
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Medical uses
Ty21a and Vi capsular polysaccharide vaccine are effective in reducing typhoid fever with low rates of adverse effects. Newer vaccines such as Vi-rEPA seem promising.
The oral Ty21a vaccine prevented one-third to one-half of typhoid cases in the first two years after vaccination, but had no benefit in the third year. The injectable Vi polysaccharide vaccine prevented about two-thirds of typhoid cases in the first year and had a cumulative efficacy of 55% by the third year. Neither vaccine is effective in children under 5 years old. Vi-rEPA vaccine, a new conjugate form of the injectable Vi vaccine, may be more effective and prevents the disease in many children under the age of 5 years. In a trial in 2-to-5-year-old children in Vietnam, the vaccine had more than 90 percent efficacy in the first year and protection lasted at least 4 years.
Schedule
Depending on the formulation it can be given starting at the age of two or five years old. Three or four doses are then given, with a dose every two days. Different authorities recommend additionally doses every three to seven years. Every 3 years for Vi polysaccharide or 7 years for Ty21a.
Ty21a can be used from age two years and older. Boosters are recommended every two years in the United States. The Vi capsular polysaccharide vaccine is licensed for use from age two years and older, and boosters are recommended every five years.
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Types
- Vi polysaccharide vaccine: Typhim Vi (Sanofi Pasteur); Typherix (GSK)
- Combined hepatitis A/Vi polysaccharide vaccine: ViATIM (Sanofi Pasteur); Hepatyrix (GSK)
- Ty21a oral vaccine: Vivotif (PaxVax)
- Activated whole cell vaccine remains available in some parts of the developing world as of 2008.
Source of the article : Wikipedia
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