US enrolls volunteers in large test of possible Zika vaccine

Henrietta Brewer
April 1, 2017

The U.S. National Institute of Allergy and Infectious Diseases (NIAID) said Friday it has begun a Phase two clinical trial of its experimental DNA vaccine created to protect against Zika virus in the United States as well as Central and South America.

The trial on the vaccine, developed by government scientists at the NIAID's Vaccine Research Center, will take place in two parts. About 2,500 healthy participants in the US and South America will be tested in areas of confirmed or potential active mosquito-transmitted Zika infection.

The University of Miami Miller School of Medicine will soon begin one of the nation's first full-scale Zika vaccine clinical trials testing the National Institutes of Health's (NIH) experimental DNA-based vaccine.

The virus is likely to become endemic - a permanent resident - in parts of south and central America, Fauci said, and it's likely to cause periodic outbreaks in the U.S.


Artist Luke Jerram looks at a jewel-like sculpture of the Zika virus in the Glass Microbiology exhibition in Bristol, England.

Florida officials say they're continuing aggressive efforts to stop the spread of the Zika virus.

Part A of Phase II will involve 90 healthy test subjects, both men and nonpregnant women, ages 18-35 years at three sites in Houston, Miami and San Juan, Puerto Rico. Pregnant women can't receive the experimental shots but women of child-bearing age can enroll. In this part of the trial, researchers will administer the vaccine at varying doses to better understand how much of the vaccine a person needs in order for it to be effective.

The other 2,400 participants are needed for Part B. All participants will receive the vaccine candidate during three separate visits that are four weeks apart. Neither the scientists nor the participants will know who received the trial vaccine.


How fast this stage of testing goes will depend on how bad outbreaks of Zika are in the countries taking part, and on how well the vaccine works, Fauci said.

"I really can't predict what the budget situation is going to be", he said. Investigators will compare the rates of confirmed cases of Zika in the placebo group and the vaccinated group to determine if the trial vaccine protects against the virus. The Zika vaccine candidate contains a single circular strand of DNA called a plasmid into which is inserted genes that encode two proteins found on the surface of the Zika virus. The results of their initial tests showed that the vaccine is safe and can induce a neutralizing antibody response against Zika virus. The Phase 2/2b trial aims to gain more safety and immune response data and determine if this immune response protects against disease caused by natural Zika infection.

The trial, which will cost $100 million, is fully funded through this phase, but Fauci said it is unclear whether there is funding for the next phase.

The NIH notes that it might add more sites down the line.


In the continental United States, of 1228 Zika-infected pregnancies, 54 babies have been born with birth defects and seven resulted in miscarriages, stillbirths or abortions, according to federal data. The prospects of more Zika cases pose an especially serious public health risk to pregnant women in the state since it's well known that the virus can cause serious and irreversible birth defects.

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