Doctors at a Philadelphia-based lab are testing a Zika Virus vaccine approved for human trials.

The vaccine is reportedly being tested in 40 people.

Doctor David Weiner of the Wistar Institute says what makes this vaccine different is that it’s entirely synthetic.

“Doesn’t grow, can’t replicate, can’t spread to other individuals,” said Weiner.

“Navy Seals rehearse, they don’t always necessarily shoot somebody. Sort of the same thing. We’re rehearsing the immune system, making them able so when they would encounter the real pathogen, they’d be prepared.”

Weiner says they are seeing a good indication that the vaccine is stimulating the generation of T-Cells that would target the Zika Virus.

The FDA will determine when and if this Zika vaccine can be used by the general public.