Researchers are one step closer to creating an approved Zika vaccine, with the first round of safety trials already underway.
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Drug companies have shown success in preclinical trials, in which they have induced immunity in mice and monkeys, indicating a greater likelihood that the vaccine could prevent infection in humans.
“In the last couple decades with modern microbiology, there’s been an explosion [in 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 1 vaccine trials, which involve a small number of volunteers. In Phase 1 trials, researchers test the safety of a drug or treatment before testing for effectiveness in large groups. Inovio Pharmaceuticals and GeneOne Life Science paired up and dosed their first human subject last week.
Currently 40 healthy volunteers are taking part in the Inovio–Gene One study, which will examine the safety of the vaccine, called GLS-5700.
The vaccine is created by isolating the DNA sequence from the Zika virus and replicating parts of the DNA sequence in the lab and then adding it to a plasmid, a tubular form of DNA found in bacteria often used to grow and administer vaccines. The viral DNA 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, when vaccinated people are exposed to the virus in the environment, their immune system will 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 1 trial is successful, it will be followed by a Phase 2 trial, which involves many more volunteers to gauge the vaccine’s safety and effectiveness. At that stage, researchers will examine patients’ blood for antibodies, which signal whether the subjects could likely fend off a Zika virus infection.
The last step before approval is a Phase 3 trial, in which 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 1 human trials for a different Zika vaccine in the fall of 2016, perhaps as early as this month. In addition to a DNA vaccine, NIAID will pursue other 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 chickenpox. The vaccine introduces an inactivated, weakened version of the virus to the body, inducing immunity. Unfortunately, live-attenuated vaccines are not safe for people who are pregnant or have a weakened immune system.
Whole-particle inactivated vaccine, which is a virus that has been killed. Although it is safer than a live-attenuated vaccine, an inactivated vaccine can create a weaker immune response, requiring subsequent booster shots.
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 and urban health resident at Johns Hopkins Hospital who is currently working at ABC News in the medical unit.