Zika Vaccine Now in First Round of Testing

Researchers are one step closer to creating an approved Zika vaccine with the first round of safety trials already underway.

Drug companies have shown success in preclinical trials where they have induced immunity in mice and monkey subjects, increasing the potential for preventing infection in humans.

"In the last couple decades with modern microbiology, there's been an explosion [in the how quickly we] test vaccines," Dr. William Schaffner, an infectious diseases expert at Vanderbilt University Medical Center, told ABC News.

Two drug companies are leading the way in Phase I vaccine trials, which involve a small number of volunteers. In Phase I trials, researchers test the safety of a drug or treatment prior to testing the effectiveness in large groups. Inovio Pharmaceuticals and GeneOne Life Science paired up and officially dosed their first human subject last week.

Currently 40 healthy volunteers are taking part in the Inovio/Gene One study that will examine the safety of the drug called GLS-5700.

The vaccine is created by isolating the DNA sequence from the virus and replicating parts of the DNA sequence in the lab and then adding it to a substance called a plasmid, a tubular form of DNA found in bacteria often used to grow and administer vaccines. The viral vaccine gets added to the plasmid, which can then be used in a vaccine to hopefully prime the immune system to create antibodies to fight Zika.

Since just portions of viral DNA are used, the virus cannot be transmitted through the vaccine.

In theory, if the vaccine works when the body is exposed to the virus in the environment, it will hopefully recognize and attack the virus.

"There's reason to be optimistic that a vaccine will work...it has to do with how the virus interacts with human host," said Schaffner. "The vaccine is more an anticipation of things we hope to go well."

If a Phase I trial is successful, it will be followed by a Phase II trial that will involve many more volunteers to gauge the vaccine's safety and effectiveness. In that situation, researchers will examine a patient's blood for antibodies that signal if a person could likely fend off a Zika virus infection.

The last step is a Phase III trial when groups of people in areas affected by the Zika virus would be given either a vaccine or a placebo and researchers would determine how effective the vaccine is at providing protection.

The National Institute of Allergy and Infectious Diseases (NIAID) plans to initiate Phase I human trials in the fall of 2016 and as early as this month. In addition to a DNA vaccine, NIAID will pursue different types of vaccines including:

-Live-Attenuated Vaccine, which is a live, but weakened form of the virus. This type of vaccine is used for diseases such as chicken pox. The vaccine introduces an inactivated, weakened version of the virus to the body which then creates immunity. Unfortunately, live-attenuated vaccines are not safe for those who are pregnant or have weakened immune systems.

-Whole-Particle Inactivated Vaccine, which is a virus that has been killed. Although it is safer than a live-attenuated vaccine, the vaccine can create weaker immune responses that require booster shots in the future.

Researchers anticipate that an effective vaccine will not be approved for public use for at least a year.

Dr. Shakira Sanchez-Collins is an Internal Medicine/Urban Health Resident at Johns Hopkins Hospital who is currently working at ABC News in the medical unit.