A vaccine to protect against the Zika virus has entered a Phase 2 trial, the first time an experimental Zika vaccine passed initial safety testing stages.

The trial tests a vaccine developed by scientists at the National institute for Allergy and Infectious Diseases (NIAID) and allows scientists to see clues as to whether the vaccine provides protection against Zika, by the end of this year, said Dr Anthony Fauci, director of NIAIAD.

The DNA-based vaccine is based on genetically engineering small chunks of DNA to include proteins from the Zika virus. Currently, there are several DNA vaccines licensed for agricultural use, but there are currently no licensed DNA vaccines for use in humans.

Zika still a threat in many countries

The trial began on 29 March at Baylor College of Medicine in Houston, one of 11 sites involved in the study. Other sites include Puerto Rico, Mexico, Costa Rico, Brazil and Peru, where Zika is prevalent.

Fauci acknowledged that public interest in Zika has waned, especially after WHO announced that the Zika threat is no longer on the global emergency list. But he said it is still critical to pursue the development of the vaccine.

It is likely the Zika virus has become or will become entrenched in parts of the Americas, Fauci said, therefore continuing to pose a risk to pregnant women who may be exposed to it as infection during pregnancy can lead to severe neurological birth defects.

"I'm totally intent on getting this vaccine to the point where it can be a usable vaccine," Fauci said, adding that the development of a Zika vaccine "a very high priority" for the NIAID.

Trial length depends on transmission rates and effectiveness of vaccine

The Phase 2 trial - called VRC 705 - will cost USD100 million, which the institute - part of the National Institutes of Health - has dedicated funding for.

If the VRC 705 is successful and a larger Phase 3 trial is needed, it is expected that some of that cost would be funded by a commercial partner. NIAID has not liaised with a large vaccine manufacturer to help develop and license the experimental vaccine, but has a couple of interested companies lined up, according to Fauci.

VRC 705 is a two-part trial with the first segment beginning last week. It involves 90 healthy volunteers -with the exception of pregnant women - all of whom will be immunised with the vaccine to determine the optimal dose.

The second segment will begin after the first and will involve 2,400 healthy volunteers, of which half will receive the vaccine and the other, a placebo. Subjects will then be monitored for approximately two years, depending on the transmission rates and how well the vaccines work.

Trial may need to be expanded in the future

If Zika continues to prevail in areas where the volunteers reside, comparing infection rates between the vaccine and placebo groups would show if the vaccine is preventing infection.

Fauci said that Zika belongs to the family of flaviviruses, which causes diseases in waves, therefore it is a possibility that transmission may taper off for a period of time after a big outbreak.

In such a possibility, the trial might have to be expanded to a larger number of 5,000 people to prove its effectiveness, especially if transmission reduces. However the transmission would be expected to resume at some point down the road. MIMS

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