A Pennsylvania drug company has launched a clinical trial of a Zika vaccine in Puerto Rico, the part of the U.S. hardest hit by the mosquito-borne virus.

Inovio Pharmaceuticals Inc. says it will be testing its DNA-based vaccine candidate on 160 adult volunteers in Puerto Rico. CEO J. Joseph Kim said Monday that if the results are promising, the company would meet with regulators next year to discuss developing the vaccine.

Inovio conducted the first vaccine trial in June with volunteers in the U.S. and Canada. It expects results later this year. The National Institutes of Health is also studying a DNA-based vaccine rather than the traditional method using a dead or weakened virus. Other vaccine candidates are also in development.

Puerto Rico has reported more than 13,000 Zika cases.