A new vaccine candidate against shigellosis, one of the leading causes of deadly diarrheal disease worldwide, showed 89 percent effectiveness in a controlled human trial, according to results published in The Lancet Infectious Diseases this summer.
The vaccine, called WRSs2 and named after the Walter Reed Army Institute of Research, was tested jointly at Cincinnati Children's Hospital Medical Center and the Emory Vaccine Center's Hope Clinic in Atlanta. NPR reported on the findings this week.
The trial enrolled 108 adults. Half received the vaccine, which consists of a weakened version of the shigella bacteria suspended in a liquid taken in two doses a month apart. The other half received salt water. In the placebo group, 81 percent of participants got sick, experiencing diarrhea and fever before receiving antibiotics.
Dr. Robert Frenck, a professor of pediatrics at Cincinnati Children's and director of its Center for Vaccine Research, co-led the trial. He described the deliberate exposure model as providing a more rigorous test of the vaccine than waiting for participants to naturally contract the illness.
Dr. Kawsar Talaat, an infectious disease physician and vaccine scientist at the Johns Hopkins Bloomberg School of Public Health, was not involved in the trial but reviewed the results. She said the 89 percent figure was difficult to dismiss given the severity of the challenge participants faced.
"So the fact that the vaccine prevented almost 90% of the illness is really remarkable," she said. "It's the best efficacy we've ever seen."
Globally, more than one million people die from diarrheal illness each year. Nearly half are children under the age of five. Chad has the highest rate of childhood deaths from the disease, with roughly one in 140 children under five dying each year. Researchers have noted that the disease receives less public health attention than its death toll warrants, a phenomenon they describe as the poo taboo.
"Throughout the world, diarrheal illness is the second leading cause of death of children," Frenck said. "And Shigella is one of the leading causes of that."
Volunteers in the trial were paid about $250 a day for roughly a week and were required to pass a quiz confirming they understood the risks. Frenck said that model made a swift and efficient trial possible. The relatively small number of participants, he acknowledged, is a limitation, but Talaat said the controlled exposure design makes the efficacy number more credible, not less.
The vaccine has not yet been approved for public use. Further trials, including studies in children and in regions where shigellosis is endemic, would be needed before it could be deployed broadly.
