* Vaccine worked best in youngest children
* Cheap vaccine provides herd immunity
BOSTON, July 22 (Reuters) - GlaxoSmithKline's
Typherix vaccine shields children as young as 2 from typhoid fever, and widespread vaccination can even protect people who have not been given the shot, according to a study published on Wednesday.
The test, conducted in two wards of an Indian slum where about 60,000 people live, was designed to see how well the Vi-type vaccine works in youngsters age 2 to 5.
Doubt about its effectiveness in this younger age group is one reason the shots, which cost as little as 50 cents, are not widely given to prevent typhoid. The potentially deadly disease comes from contaminated food and water, and kills 216,000 to 600,000 people worldwide each year.
At the end of 2004, 37,673 children and adults were inoculated with Typherix or, for comparison purposes, GlaxoSmithKline's Havrix vaccine for hepatitis A. Several companies make the typhoid vaccine.
It worked in 61 percent of the people exposed to the disease, said the team led by Dr. Dipika Sur of the National Institute of Cholera and Enteric Diseases in Kolkata, India.
It was most effective in children under 5, where the protection rate was 80 percent.
"This protection for children under the age of 5 years is important because this age group has been shown to be at high risk for typhoid fever in many areas where the disease is endemic," the researchers wrote in the New England Journal of Medicine.
The protection level dropped to 56 percent for 5- to 14-year-olds, and was 46 percent for those 15 and over.
When enough people were vaccinated, spread of the disease slowed through the community, protecting even people who did not receive the shots, a phenomenon known as herd immunity.
In the community as a whole, immunization blocked 57 percent of typhoid cases among both vaccinated and unvaccinated people, the Sur team concluded.
"This is important new information," Dr. Myron Levine of the University of Maryland School of Medicine wrote in a commentary.
"The indirect protection of nonvaccinated persons by the Vi vaccine further bolsters the case for school-based immunization to control endemic typhoid, since one might expect some indirect protection of preschool children as well," he wrote.
In addition to the Vi vaccine, which sensitizes people to a part of the typhoid bug, there is an oral Ty21a vaccine that uses a chemically weakened strain of the bacteria.
However the Ty21a capsule or liquid must be given in at least three doses, which poses logistical difficulties except in organized settings such as schools.
"The time has come to implement use of these vaccines vigorously and monitor the effect of such intervention," wrote Levine.
Typhoid fever can last for weeks or months without antibiotic treatment and up to 20 percent of cases can die from the disease.
Editing by Maggie Fox
Our Standards: The Thomson Reuters Trust Principles.