According to the U.S. Centers for Disease Control and Prevention, about 16 million people worldwide develop typhoid each year, and 600,000 die from it. Roughly 400 cases of typhoid fever occur in the U.S. each year, about 70 percent of which are acquired by Americans traveling abroad. More than 90 percent of the typhoid strains present in the area are resistant to the antibiotics used to treat the disease. The approach involves chemically linking a polysaccharide from the disease-causing bacteria with a protein molecule. Ordinarily, the polysaccharide would slip past the defenses of a child s immature immune system, but adding the protein to the polysaccharide allows the immune system to produce antibodies that inactivate the bacteria.
Antibodies are immune system proteins that recognize a particular substance.
Together with another protein called complement, antibodies begin the first steps in the complex sequences of events by which the immune system destroys disease-causing organisms. The children received two injections, six weeks apart. Half received the vaccine, and the other half, a placebo. Over the next two years, their physicians observed both groups. Those who developed typhoid fever received the standard treatment of antibiotic therapy for the disease.