Clinical trial for Zika vaccine shows promise. But will it prevent infection?

An experimental Zika vaccine developed by scientists at the National Institute of Allergy and Infectious Diseases is safe and induces an immune response in healthy adults, according to findings from an early stage clinical trial published Monday in The Lancet, a medical journal.

The DNA-based experimental vaccine is now in the second phase of clinical trials to determine its safety and effectiveness at preventing infection with Zika virus.

Government scientists with the NIAID, part of the National Institutes of Health, developed the experimental vaccine soon after a 2015 outbreak of Zika in northwest Brazil revealed that infection during pregnancy could lead to birth defects.

Scientists developed the experimental vaccine, which includes a small piece of DNA called a plasmid, by inserting genes into the plasmid that encode two proteins found on the surface of the Zika virus. After the experimental vaccine is injected into muscle, the body produces proteins that mimic the Zika virus and trigger the body’s immune response.

Researchers tested two different versions of the vaccine and found that healthy adult volunteers tolerated them well in both trials, although some participants who received injections reported feeling tenderness, swelling and redness at the injection sites. Other participants received the vaccine from a needle-free injector that pushes fluid into the arm muscle.

All participants received two or three 4-milligram doses of the experimental vaccine. Scientists then analyzed blood drawn from the participants four weeks after their final vaccinations. They found that 60 to 89 percent of the participants generated an immune response to one version of the experimental vaccine while 77 to 100 percent of the volunteers showed an immune response to the second version.

Participants who received the second version of the experimental vaccine via the needle-free injector all generated an immune response and had the highest levels of Zika-neutralizing antibodies in their blood. Scientists also found that participants who received the experimental vaccine in a split dose given in both arms had a more robust immune response than those who received a full dose in one arm.

Government researchers concluded that the second version of the experimental vaccine showed the most promise and they advanced it into an international trial in March 2017. That trial aims to recruit 2,490 healthy volunteers between the ages of 15 and 35 in areas where mosquitoes are spreading Zika, including Miami.

Initially, the University of Miami Miller School of Medicine was designated as the local site for the clinical trial. However, NIAID said that due to operational delays at the site, UM was not activated for participation in the trial, so it did not enroll or vaccinate volunteers.

Scientists selected a new site in Miami at QPS-Miami Research Associates, a privately owned clinical research center. QPS is still recruiting volunteers for the experimental Zika vaccine. Interested persons should contact Maria Soto at 305-279-0015, ext. 4206 or by email at

Florida health officials have confirmed a total of 229 cases of Zika statewide as of Dec. 4. The first local case of 2017 spread by mosquitoes in Florida was reported in October in Manatee County. Miami-Dade’s first local case of Zika this year was confirmed in November.

In addition, one sexually transmitted Zika infection was reported in August, though that case was considered to be travel related because the infected person’s partner had recently gone to Cuba, where mosquitoes are reportedly spreading the virus.

Another 195 Zika infections recorded in Florida this year were acquired by people who had traveled to areas where the virus is actively spreading, according to the health department, while 32 cases are attributed to “undetermined exposure in 2016.”

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