Scientists expect to test the first experimental Zika vaccine on humans in the coming weeks, after the pharmaceutical company Inovio received approval from the US Food and Drug Administration to start a small clinical trial.



Zika, which is a mosquito-borne virus, can cause severe birth defects, is linked with the muscle paralysis syndrome Guillain-Barré, and is now endemic in much of Latin America.

Inovio plans to enroll 40 healthy adults in its trial. Research will focus on safety, dosage and the body’s immune response to the vaccine, the company said. Such research is typical of a “phase one” trial, as scientists call such early work.

Researchers would probably need several trials to prove the vaccine is safe, effective and provided at the right dose. Testing on “small and large animals” has already occurred, the company said. The experimental vaccine, called GLS-5700, uses synthetic fragments of virus DNA to provoke an immune response in the body.

“Always, the first vaccine to go into clinical trial is important,” said Anna Durbin, an associate professor of international health at Johns Hopkins, and a member of a National Institutes of Health team working separately to develop a Zika vaccine.

“It means the FDA has reviewed it, and I’m sure is formulating questions and getting ready for additional candidates to submit their investigational drug applications,” she said. “It shows progress and momentum, and we just need to keep momentum going.”

Scientists first started sounding the alarm about Zika early in 2016, when a link appeared with microcephaly, an uncommon birth defect where children are born with abnormally small heads and severe developmental impairment.



By April, scientists at the Centers for Disease Control and Prevention confirmed Zika was the cause of the birth defects. By June, the World Health Organization reported more than 1,500 cases of microcephaly in Brazil, which has by far the largest number, and that mosquitoes in more than 60 countries carried the disease.

Most victims do not experience the mild, cold-like symptoms the virus produces, but some may develop the muscle-paralyzing Guillain-Barré syndrome. The disease is spread primarily through bites of the Aedes aegypti mosquito, but can also be spread sexually. There is no vaccine or treatment for Zika, and the WHO has warned women in areas where the virus is endemic to delay pregnancy.

The vaccine being developed by Inovio is what is known as a “DNA vaccine”. Researchers that the Guardian spoke with said they did not believe any DNA vaccines were currently approved for use in humans in the US. The FDA was unable to confirm this by publication.



DNA vaccines were first developed about two decades ago, and showed great promise in animal models, but researchers have struggled to replicate the long-term immunity provided by other vaccine production methods.

Some of the first trials of DNA vaccines were conducted in the 1990s, and focused on diseases such as HIV and the flu, according to the Oxford journal Clinical Infectious Diseases. In theory, the DNA vaccines would be simpler to produce and generate fewer side-effects.

Currently, many vaccines are produced through what is called “live attenuation”, or reproducing a strain of “wild” vaccine in the laboratory to weaken it to the point that it is safe to administer. The current measles vaccine is one example of a live-attenuated vaccine. As of 2008, only four DNA vaccines were approved by the FDA, all for veterinary use.

Even if Inovio is able to make an effective vaccine, researchers said, the prospect of getting it on the market soon is unlikely.

“What is not really being said is that once phase one trials are completed, it is likely that progress towards licensure will slow significantly,” said Dr Peter Hotez, dean of the National School of Tropical Medicine and head of pediatric tropical medicine at Baylor College in Houston. That city has been identified as one of the Gulf coast areas where Zika could spread rapidly if it becomes endemic in the local mosquito population.

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“The FDA or other regulatory bodies will need to see trials to ensure that the vaccine does not induce Guillain-Barré syndrome, as does the Zika virus itself,” said Hotez. He added that “since the vaccine would likely be needed for pregnant women or women who are about to become pregnant, the FDA will want to see extensive safety data in these populations”.

Predicting how long it will take to develop the vaccine is also difficult, said Karen Kotloff, a pediatrics professor and head of the division of infectious disease at the University of Maryland school of medicine. Kotloff also serves on the FDA’s vaccines and related biological products advisory committee.

“The average time to take a vaccine from the laboratory bench to somebody’s arm is about 10 to 15 years,” said Kotloff, “and there is a wide range on that, so it can be substantially longer.”

As of March, around 15 pharmaceutical companies were attempting to develop a Zika vaccine, the Wall Street Journal reported.

In the continental US, 755 cases have been reported, all linked to travel. But mosquitoes in American territories in the Caribbean now carry the disease, and more than 1,400 cases of Zika have been reported there, according to the CDC.

Inovio, based in Pennsylvania, has partnered with the South Korean-based GeneOne Life Sciences Inc and several Canadian and American researchers, such as the University of Pennsylvania and the Defense Advanced Research Projects Administration, to develop the vaccine.