The first vaccine aimed at stemming the spread of the Zika virus is expected to start its first phase of human trials in the coming weeks.

"The incidences of viral infection and medical conditions caused by the virus are expanding, not contracting," said Dr. J. Joseph Kim, president and CEO of the Pennsylvania-based Inovio Pharmaceuticals Inc. "As of May 2016, 58 countries and territories reported continuing mosquito-borne transmission of the Zika virus."

The pharmaceutical company announced Monday that it and Seoul, South Korea-based GeneOne Life Science Inc. had received approval to start trials on Innovio's Zika DNA vaccine. The companies did not say exactly when the trials will start, although Kim said scientists expect to have preliminary results from the first tests "later this year."

If the vaccine is successful, it's unclear how long it would take for it to hit the market. Dr. Marie-Paule Kieny, the World Health Organization's assistant director general for health systems and innovation, estimated in February that it would take 18 months before a Zika vaccine could see a large-scale trial.

The Innovio trial will include 40 "healthy subjects" who will get different doses of the vaccine.

No vaccine or therapy currently exists for Zika, a mosquito-borne illness that can cause fevers and rashes in infected people. It rarely requires hospitalization, although scientists have found links between the virus and a pair of serious and rare conditions.

Pregnant women who have Zika can give birth to babies suffering from microcephaly, a birth defect that gives newborns smaller than average heads. It can also cause Guillain-Barré syndrome, a rare condition that causes temporary weakness and sometimes paralysis.

The disease can also be sexually transmitted.

At least six pregnant women in the U.S. have reported Zika-related complications, according to numbers released last week by the Centers for Disease Control and Prevention. Of those, three lost or terminated their pregnancies because of the virus.

Of the 756 cases of Zika infection reported in the U.S., all but one was contracted abroad. The remaining infection was contracted in a laboratory, according to the CDC.

Three of those cases resulted in Guillain-Barré syndrome.

In addition to Innovo, at least 15 other companies are working to develop a Zika vaccine, according to WHO.