Novel typhoid vaccine surpasses old ones
By Nathan Seppa
Although many people in industrialized countries think of typhoid fever as a
scourge of bygone times, the disease strikes more than 16 million people worldwide
every year. Adults immunized with the best available vaccines still face a 30
percent risk of contracting typhoid if they come into contact with Salmonella
typhi, the bacterium that causes the disease. The vaccines impart even weaker
protection to young children.
A study of Vietnamese children 2 to 5 years old now provides the best showing ever
for a typhoid vaccine, says study coauthor Feng Ying C. Lin, a pediatrician at the
National Institutes of Child Health and Human Development (NICHD) in Bethesda, Md.
The new vaccine can slash typhoid risk after contact with the pathogen to less
than 10 percent.
Beginning in 1997, Lin and her colleagues gave 11,091 children living in a
typhoid-infested area of the Mekong River delta two injections, 6 weeks apart.
Half the children received the vaccine, and the others got shots of saline water.
Only 4 of those vaccinated contracted typhoid during the next 27 months, compared
with 47 of those not vaccinated, the researchers report in the April 26 New
England Journal of Medicine. The disease was milder in the vaccinated children
than in the others. A group that had received only one vaccination showed
considerable protection as well.
The new vaccine links a sugar molecule found on the surface of S. typhi with a
harmless, genetically engineered version of a protein called exotoxin A from
another bacterium. This sugar-protein duo arouses the immune system to churn out
antibodies against the typhoid bacterium, says study coauthor Shousun C. Szu, a
biochemist at NICHD. Three-year data from the study suggest the protection is long
lasting, Lin says. Other vaccines elicit lower antibody concentrations and wear
off faster, she says.
If the new vaccine also proves effective in babies less than 2 years old, it
could play an important role in controlling the disease in areas where it is
endemic, says Richard L. Guerrant of the University of Virginia in
Charlottesville. He also expects the vaccine to protect older children and adults.
Typhoid spreads when bacteria in feces contaminate drinking water or food. The
partial effectiveness of a single vaccination means quick distribution of the new
vaccine could slow the disease’s spread during outbreaks, Lin says.
