Inovio Pharmaceuticals and GeneOne Life Science’s Zika vaccine has shown promise in an early human trial.

All 40 healthy volunteers in the study developed Zika-specific antiboides after three doses, researchers said.

The companies’ GLS-5700 is a DNA-based vaccine that is made by reproducing sections of the Zika virus genome and loading them onto a plasmid, unlike standard vaccines that usually use inactivated or killed versions of a virus.

After the vaccine is injected into a patient, a device is used to generate electrical impulses that create small pores in cells that allow the DNA to get inside.

Sanofi ended development on its more traditional Zika vaccine last month, while Takeda is still working on its own product.