Vi capsular polysaccharide vaccine

The Vi capsular polysaccharide vaccine (or ViCPS) is one of two vaccines recommended by the World Health Organisation for the prevention of typhoid (the other is Ty21a). It was first licensed in the US in 1994 and in made from the purified Vi capsular polysaccharide from the Ty2 "Salmonella" Typhi strain.

The vaccine is only 60 to 80% protective and the traveller should still be warned to take all usual precautions (careful hygiene, hand washing and food preparation).

Indications

The vaccine may be used in endemic areas in order to prevent typhoid. It is also commonly used to protect people who are travelling to parts of the world where typhoid is endemic.

Advice for travellers is available from:
* [http://wwwn.cdc.gov/travel/| Centers for Disease Control and Prevention (US)]
* [http://www.travelhealth.co.uk/| Travel Health (UK)]
* [http://www.who.int/ith/en/| World Health Organisation (International)]

Dosing

The vaccine is injected either under the skin or into a muscle at least seven days before travelling to the typhoid-affected area (the CDC recommend 14 days). The vaccine is not effective in children under the age of two; children under the age of two would normally have all their food regulated by their parents and should therefore be expected to be at low risk of exposure to typhoid.

To maintain immunity, the vaccine should be repeated every three years.

Efficacy and duration of protection

In a randomised controlled trial of more than 11,000 children in South Africa, the vaccine was 64% efficacious after 21 months and 55% efficacious 3 years after vaccintion; more than half the children still had protective levels of antibodies 10 years after vaccination. [cite journal|author=Keddy KH, Klugman KP, Hansford CF, Blondeau C, Bouveret le Cam NN|title="Salmonella typhi" Vi capsular polysaccharide vaccine in South African school children ten years after immunization|journal=Vaccine|year=1999|volume=17|issue=2|pages=110–113|pmid=9987143|doi=10.1016/S0264-410X(98)00160-1] A randomised controlled trial of 6900 subjects in Nepal showed that the vaccine conferred 72% protection after 17 months. [cite journal|author=Acharya IL, Lowe CU, Thapa R, "et al."|title=Prevention of typhoid fever in Nepal with the Vi capsular polysaccharide of "Salmonella typhi". A preliminary report|journal=N Engl J Med|volume=317|year=1987|pages=1101–1104|pmid=3657877] A randomised controlled trial of 131,000 subjects in southwestern China showed the vaccine to be 69% protective over a 19-month observation period. Follow up of this population in the third year after vaccination showed evidence of protection in approximately 50% of the vaccinees. [cite journal|author=Yang HH, Kilgore PE, Yang LH, "et al."|title=An outbreak of typhoid fever, Xing-An county, People's Republic of China, 1999: estimation of the field effectiveness of Vi polysaccharide typhoid vaccine|journal=J Infect Dis|year=2001|volume=183|issue=12|pages=1775–1780|pmid=11372030|doi=10.1086/320729]

Trade names

*Typhim Vi (manufactured by sanofi pasteur)

See also

*Ty21a

References