In development for 20 years, a vaccine for the dengue virus is being released by French pharmaceutical giant Sanofi. Primarily a mosquito-spread illness, dengue fever isn’t widely known in the U.S., where it occurs only in South Florida and Puerto Rico. A flu-like disease, the only treatments are symptomatic and in about two percent of cases, the disease can be life-threatening. “The biggest issue with the disease is not the severity,” says Kasia Hein-Peters, vice president....