NIH begins testing experimental Zika vaccine in humans

Last Updated Aug 3, 2016 7:39 PM EDT

Government officials are beginning to test an experimental vaccine intended to prevent Zika virus infection, the National Institute of Allergy and Infectious Diseases (NIAID) announced today.

The early-stage study will evaluate the vaccine's safety and ability to generate an immune system response in at least 80 volunteers, ages 18 to 35.

"If this vaccine works, it will be a very big deal," said CBS News chief medical correspondent Dr. Jon LaPook.

The news comes just days after Florida health officials confirmed the first cases of Zika locally transmitted by mosquitoes in the mainland U.S. At least 15 people have been infected, primarily in the Wynwood neighborhood in Miami-Dade County. The CDC issued a travel advisory warning pregnant women to avoid a one-square-mile area where the infections are believed to have occurred.

Though in most people who are infected, Zika virus produces only mild symptoms -- or no symptoms at all -- it is particularly worrisome for pregnant women because it has been found to cause a severe birth defect called microcephaly in babies.

According to the CDC, Zika is actively spreading in more than 50 countries and territories, mostly in Latin America and the Caribbean. It is primarily spread by tropical mosquitoes, and can also be sexually transmitted.

There is currently no vaccine or cure for the virus.

"A safe and effective vaccine to prevent Zika virus infection and the devastating birth defects it causes is a public health imperative," NIAID Director Anthony S. Fauci, M.D. said in a statement. "NIAID worked expeditiously to ready a vaccine candidate, and results in animal testing have been very encouraging. We are pleased that we are now able to proceed with this initial study in people. Although it will take some time before a vaccine against Zika is commercially available, the launch of this study is an important step forward."

The experimental vaccine uses a similar approach to that used by another investigational vaccine developed by NIAID for West Nile virus. That shot was found to be safe and induced an immune response when tested in a preliminary trial.

The potential Zika vaccine includes a small, circular piece of DNA -- called a plasmid -- which scientists engineered to contain genes that code for proteins of the virus. When the plasmid is injected into the arm, muscle cells read the genes and make Zika virus proteins, which self-assemble into virus-like particles. The body then develops an immune response to these particles.

The NIAID emphasizes that DNA vaccines do not contain infectious materials and thus cannot cause a person to become infected with Zika.

This type of vaccine has also been shown to be safe in previous clinical trials for other diseases.

"DNA or gene-based vaccines induce antibodies, but they also can activate the cell-mediated immune response, which ultimately could yield strong and durable protection against disease," said John Mascola, M.D., director of NIAID's Vaccine Research Center.

The testing will take place at three sites in the United States: the National Institutes of Health Clinical Center in Bethesda, Maryland; the University of Maryland's Center for Vaccine Development in Baltimore; and Emory University in Atlanta

All of the participants will be given different doses of the vaccine, with none getting placebos.

Initial results are expected by the end of 2016. If the data shows the vaccine is safe and has a favorable immune response, NIAID plans to begin testing it in Zika-endemic countries early next year.

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