Scientists have begun a clinical trial of two vaccines that may prevent Shigella infection, announced the National Institutes of Health Wednesday. The government-funded study will examine the effect of two different but related vaccines on 90 healthy adults ages 18 to 45 years old. Shigellosis, the disease caused by infection with Shigella bacteria, is an intestinal disease that causes fever, abdominal cramps, diarrhea, nausea and vomiting. Shigella causes an estimated 400,000 diseases in the United States each year, according to the Centers for Disease Control and Prevention. On a global scale, the World Health Organization estimates that the bacteria causes 90 million serious cases of disease and leads to 108,000 deaths per year. Death from shigellosis occurs predominantly among people in developing countries, especially in children under age five. While shigellosis is usually treated with antibiotics, many drug-resistant strains of Shigella are now emerging. “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 in a statement Wednesday. “They’ve become very good at evading the human immune response and causing significant illness, so developing vaccines and better treatments is critical.” The two new vaccines – called WRSs2 and WRSs3 – target the most common of the four strains of the bacteria — Shigella sonnei. Both have been found to be safe and effective when used on guinea pigs and nonhuman primates, according to an NIH press release. In this study, researchers will look to see whether the vaccines generate an immune response in subjects without jeopardizing their safety. An earlier version of these vaccines, WRSs1, was found to meet both these criteria in human trials in the U.S. and Japan. However, these newer vaccines are not expected to cause the mild diarrhea experienced by some patients to whom WRSs1 was administered. Patients in this study will be monitored closely. All will be admitted to inpatient care immediately after receiving the vaccine, and will begin a course of antibiotics eight days later, or earlier if symptoms of the disease appear. Patients will stay in the hospital for up to 13 days, and will submit stool samples three times after being discharged, at 14, 28 and 56 days after receiving the vaccine. The research is funded by the National Institute of Allergy and Infectious Diseases and will be led by Dr. Robert W. Frenck, Jr., director of clinical medicine at Cincinnati Children’s. WRSs1, WRSs2 and WRSs3 were all developed at the Walter Reed Army Institute of Research.