Zika vaccine clinical trial starts in humans

Inactivated virus used to create drug, researchers say

By Daniel Chang

With Florida health officials reporting more mosquito-borne Zika infections in Miami-Dade, including one new case confirmed Monday, scientists with the Walter Reed Army Institute of Research launched the first of five early-stage clinical trials that they hope will lead to the development of a vaccine against the virus.

A Zika vaccine is still two to three years away from public availability, according to scientists, but most vaccines have traditionally taken a decade or longer to develop. The shorter time frame is due in part to lessons learned from prior infectious disease outbreaks.

Kayvon Modjarrad, a physician researcher and associate director for emerging infectious disease threats at the Walter Reed institute, or WRAIR, said scientists developed the trial vaccine, called Zika purified inactivated virus, or ZPIV, using the same technology they used to create a Japanese encephalitis vaccine licensed in 2009.

There are currently three Zika vaccine candidates undergoing human clinical trials, but ZPIV is the only one that uses a weakened or dead virus to provoke an immune system defense.

The other two candidates are DNA vaccines that also elicit immune system response by using genetically engineered DNA that stimulate cells. They are being tested separately in clinical trials by the National Institutes of Allergy and Infections Diseases and by Inovio Pharmaceuticals — though no DNA vaccine has ever been licensed for human use.

After preclinical studies in early July showed that two doses of ZPIV, administered four weeks apart, provoked a protective immune response to Zika in rhesus monkeys, the vaccine candidate advanced to human trials.

Currently, there are five different clinical trials scheduled using ZPIV, Modjarrad said, including one by St. Louis University researchers to determine the optimal dose of vaccine to be used in larger studies.

Other ZPIV studies will evaluate the safety and effectiveness of administering the vaccine candidate in a shortened time period, and its ability to prevent Zika in people who have been naturally exposed to Zika or dengue. A fifth trial will examine the effectiveness of using the DNA and ZPIV vaccine candidates together.

For the ZPIV human clinical trial launched Monday, WRAIR scientists will recruit 75 healthy adult volunteers who have never been infected with any of a related group of viruses, including yellow fever, dengue, West Nile, Japanese encephalitis and Zika.

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