By Jennifer Nachbur
With spring temperatures finally here, mosquito season is just around the corner and with it, the threat of West Nile virus – the leading vector-borne cause of viral encephalitis (inflammation of the brain) in the U.S. West Nile Virus (WNV) first reached the United States in 1999 when six patients were seen in a New York City hospital with fever and new neurologic symptoms. By 2010, the number of adults who had been infected with WNV in the U.S. was estimated to be nearly three million, with 13,000 cases of West Nile neuroinvasive disease – the more severe form of the disease.
Almost half of these cases occurred in adults over the age of 60. The second largest U.S. outbreak of WNV occurred in 2012, with the CDC reporting 5,674 cases and 286 deaths – the highest death rate attributed to the virus since its arrival in the United States in 1999. Currently, a licensed vaccine for the prevention of human disease doesn’t exist, and strategies for controlling the virus have been limited to mosquito eradication.
This month, the Vaccine Testing Center at the University of Vermont is launching a phase one West Nile Virus vaccine trial, led by the University of Vermont Medical Center infectious disease specialists Kristen Pierce, M.D., assistant professor of medicine, and Beth Kirkpatrick M.D., professor of medicine, which aims to determine effectiveness of the vaccine in the most vulnerable population.
Cases of WNV infection have been reported in all of the 48 continental states, including Vermont. While many people infected are without symptoms, a small percentage (less than one percent) can develop severe disease, such as encephalitis or meningitis (inflammation of the brain or lining of the brain and spinal cord) or hepatitis. Most cases of severe disease occur in people over 50 years of age. In fact, of the 13,000 cases of West Nile neuroinvasive disease in 2010, almost half of these occurred in adults over age 60. This new vaccine trial, which is taking place at UVM and Johns Hopkins University, will assess the vaccine’s effectiveness in building immunity in healthy adults between 50 and 65 years of age. The vaccine was previously tested at Johns Hopkins in adults aged 18 to 50 and was well-tolerated and effective in producing an immune response.
The study uses a National Institutes of Health-developed, live-attenuated WNV vaccine using recombinant DNA technology. Pierce refers to it as a “chimeric” vaccine; pieces of the dengue virus (which is similar to WNV), minus its virulence factors, serve as the vaccine’s replicative engine, but the vaccine’s phenotype – or characteristics – come from the West Nile Virus. The year-long study includes an initial vaccination with the experimental vaccine, followed by a second vaccination six months later.