Researchers have launched an early-stage human clinical trial of two related candidate vaccines to prevent infection with Shigella, bacteria that are a significant cause of diarrheal illness, particularly among children. The Phase I clinical trial, funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, will evaluate the vaccines for safety and their ability to induce immune responses among 90 healthy adults ages 18 to 45 years. The trial is being conducted at the Cincinnati Children's Hospital Medical Center, one of the eight NIAID-funded Vaccine and Treatment Evaluation Units in the United States.
Shigella infection, called shigellosis, is an intestinal disease spread via contact with infected feces, by consumption of contaminated food or water or by contact with a contaminated surface. Symptoms include diarrhea, abdominal pain, fever, nausea and vomiting. In healthy adults, the infection generally clears on its own in five to seven days, but if left untreated, can lead to hospitalization or death, especially among young children and adults with weakened immune systems.
According to the World Health Organization, shigellosis causes roughly 90 million cases of severe disease each year and 108,000 deaths, most of which occur in the developing world and affect children under 5 years of age. In the United States, 14,000 shigellosis cases are reported annually, with most cases occurring among children ages 1 to 4 years.
Antibiotics are the standard treatment for patients with shigellosis, but drug-resistant strains of the bacterium are becoming more common.
"It seems that Shigella bacteria know our immune system better than we do," said William Alexander, Ph.D., a program officer in NIAID's Enteric and Hepatic Diseases Branch, Division of Microbiology and Infectious Diseases. "They've become very good at evading the human immune response and causing significant illness, so developing vaccines and better treatments is critical."
Led by principal investigator Robert W. Frenck, Jr., M.D., director of clinical medicine at Cincinnati Children's, the new clinical trial will evaluate two related candidate vaccines, known as WRSs2 and WRSs3, which have been found to be safe and effective when tested in guinea pigs and nonhuman primates. Both target Shigella sonnei, one of the bacteria's four subtypes and the cause of most shigellosis outbreaks in developed and newly industrialized countries. Though neither candidate vaccine has been tested in humans, a precursor to both, known as WRSs1, was found to be safe and generated an immune response in small human trials in the United States and Israel. This early work was supported by NIAID, the U.S. Department of Defense and the Walter Reed Army Institute of Research. All three versions of the vaccine were developed by researchers at the Walter Reed institute.