A typhoid vaccine proved effective in the slums of India, where it not only helped prevent infection in children who received it, but also those in close contact who were unvaccinated, a new study found.

The findings may bolster the World Health Organization's push to start vaccine campaigns in poor countries against this often-fatal bacterial disease.

The vaccine was 80 percent effective in preventing typhoid fever among children ages 2 to 5, researchers found. Among unvaccinated neighbors who were in contact with the immunized children, the vaccine offered 44 percent protection.

Typhoid fever is a serious health threat in the developing world where it affects some 22 million people a year. Between 200,000 to 600,000 die annually of the disease, which is spread through contaminated food and water or through close contact with an infected person.

The bug is carried in the intestinal tract and bloodstream. Symptoms include high fever, weakness and stomach pains.

Antibiotics have long been used to treat typhoid fever, but the recent emergence of drug-resistant strains have made the disease harder to treat. Vaccines are also available, but are not widely used in public health programs because of questions surrounding their effectiveness in young children.

In the new study, researchers recruited 37,673 slum-dwellers aged 2 years or older in Calcutta, India. Study participants randomly received a dose of the typhoid vaccine or an inactivated hepatitis A vaccine and were followed for two years.

Overall, the vaccine was 61 percent effective. Protection was higher — 80 percent — among immunized young children.

Results were published in Thursday's New England Journal of Medicine. The study was funded by the Bill and Melinda Gates Foundation and coordinated by the Seoul-based International Vaccine Institute.

GlaxoSmithKline PLC provided the vaccine used in the research, but did not fund the study. Several researchers reported receiving fees and support from the drug maker.

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New England Journal: http://www.nejm.org