Zika Vaccine Trial: Too Little, Too Late?

The National Institute of Allergy and Infectious Diseases (NIAID) announced Wednesday it has launched a clinical trial of a vaccine intended to prevent Zika virus infection. This comes at the same time as another announcement: The Centers for Disease Control and Prevention updated its travel advisories to include Antigua and Barbuda as well as Turks and Caicos Islands (U.K.).

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The advisory encourages women who are pregnant to avoid these locations, as local transmission of the virus is now occurring. If you must be in these areas, you’re advised to take every precaution to avoid mosquito bites and to either use condoms or avoid having sex.

Mosquitoes that spread Zika are aggressive daytime biters — though they also bite at night. There is no vaccine or medicine for the Zika virus. Not yet, anyway.

The early-stage study announced today will evaluate the new experimental vaccine’s safety and ability to generate an immune system response in participants — if all goes well, Phase 2 would start next year in Zika-endemic countries. At least 80 healthy volunteers ages 18-35 years at three study sites in the United States, including the NIH Clinical Center in Bethesda, Maryland, are expected to participate in the trial.

Scientists at NIAID’s Vaccine Research Center (VRC) developed the investigational vaccine — called the NIAID Zika virus investigational DNA vaccine — earlier this year. The study is part of the U.S. government’s response to the ongoing outbreak of the virus in the Americas. The CDC says that more than 50 countries and territories have active Zika virus transmission.

In the United States and its territories, more than 6,400 Zika cases have been reported.

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Up to 1.65 million childbearing women in Central and South America however, could become infected by the Zika virus by the end of the first wave of the epidemic, according to estimates from scientists from the U.S. and U.K.

Researchers from the WorldPop Project, Flowminder Foundation at the University of Southampton, the University of Notre Dame, and the University of Oxford recently stated they have also found that over 90 million infections could result from the initial stages of the spread of Zika across Latin America and the Caribbean.

While most Zika infections are usually asymptomatic, some people experience mild illness lasting about a week. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly, as well as other severe fetal defects of the brain and other organs.

“A safe and effective vaccine to prevent Zika virus infection and the devastating birth defects it causes is a public health imperative,” said Anthony S. Fauci, M.D., NIAID director, 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 investigational Zika vaccine includes a small, circular piece of DNA — called a plasmid — that scientists engineered to contain genes that code for proteins of the Zika virus. When the vaccine is injected into the arm muscle, cells read the genes and make Zika virus proteins, which self-assemble into virus-like particles. The body mounts an immune response to these particles, including neutralizing antibodies and T cells.

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DNA vaccines do not contain infectious material, the CDC states — so they cannot cause a vaccinated individual to become infected with Zika. They have been shown to be safe in previous clinical trials for other diseases, officials add.

The Phase 1 clinical trial, called VRC 319, will divide volunteers randomly into four study groups of 20 people each. All participants will receive a vaccination at their first visit via a needle-free injector that pushes the vaccine fluid into the arm muscle.

Half the participants will receive an additional vaccination eight or 12 weeks later. The remaining participants will receive two additional vaccinations at varying times weeks later. All participants will receive the same dose at each vaccination and return for follow-up visits within a 44-week time period after the first vaccination.

The study team will review patient data daily and weekly to monitor safety. Initial safety and other data from the Phase 1 trial are expected by January 2017.