Pharmaceutical company Inovio just received approval from the U.S. Food and Drug Administration (FDA) to start early-stage human trials for an experimental Zika vaccine, NBC News reports. But researchers say an effective vaccine against the mosquito-borne and sexually transmitted virus is still months, if not years, away.


Zika’s spread across Latin America and the Caribbean has been swift, affecting an estimated 3 million to 4 million people in 23 countries during the last two years. In grown adults, the virus usually causes only a mild infection and often no symptoms at all. But Zika can cause serious birth defects if a pregnant woman becomes infected.


Inovio, the Pennsylvania-based company behind the new vaccine, uses two new technologies: synthetic DNA and a new delivery system that uses an electronic pulse to open up immune cells to better absorb the vaccine. Recent tests in monkeys showed that the vaccine stimulated an immune response against the Zika virus that should protect against infection. Inovio plans to dose its first human subjects in a Phase I clinical trial during the next few weeks and will post interim results later this year.


Additionally, the National Institute for Allergy and Infectious Diseases is currently working on a series of slightly different government-sponsored Zika vaccines that are nearly ready for testing. In the meantime, U.S. health officials are warning pregnant women and those who might become pregnant to stay out of Zika-affected areas and to use protection when having sex with partners who may have put themselves at risk of infection.


So far, the United States has reported 820 Zika infections, most of which have been travel-related. In addition, 11 sexually transmitted Zika infections were recently discovered. But to date no locally acquired mosquito-borne cases of Zika have been reported in this country.


To learn more about the Zika virus, click here.