SAN JUAN, Puerto Rico (AP) - A Pennsylvania drug company has launched a clinical trial of an experimental Zika vaccine in Puerto Rico, the part of the U.S. hardest hit by the virus.

Inovio Pharmaceuticals Inc. will be testing its DNA-based vaccine candidate on 160 adult volunteers in Puerto Rico. If the results are promising, the company would meet with regulators next year to discuss plans to develop the vaccine.Inovio conducted the first vaccine trial in June.