The U.S. Army vaccinated 75 healthy volunteers with an experimental Zika vaccine this week, the Department of Defense confirmed on Tuesday.
Walter Reed officials announced through a press release that a clinical trial began Monday, where 75 participants were vaccinated with a Zika virus vaccine that the institute’s scientists developed earlier this year.
The purified, inactivated Zika virus vaccine, called ZPIV, is being tested at Walter Reed Army Institute of Research’s Clinical Trial Center in Silver Spring, Maryland. It will be tested first in a Phase 1 trial, which will test the safety and immunogenicity, or the ability of the vaccine to trigger an immune response in the body.
Army Colonel Nelson Michael, director of Walter Reed’s Military HIV Research Program and co-lead of the Zika program, said in a statement that the Army had moved from recognizing Zika virus as a threat to producing the vaccine to testing it in animals and ruling it safe for human trials in only a 10-month period. They assured the public that this was safe since they have “extensive experience with this vaccine platform” and “longstanding investments in the understanding and mitigation of flaviviruses like yellow fever.”
The study is part of the Defense Department’s response to the ongoing Zika outbreak in North and South America and Southeast Asia. There are concerns with service members being infected with Zika virus during deployment and travel but also in the continental United States, since most military installations are concentrated in southern states where climate conditions and mosquito populations favor Zika transmission.
The Centers for Disease Control and Prevention says that as of November 2, there have been 149 cases of Zika infection confirmed in the military health system, including four pregnant service members and one pregnant family member.
Zika virus is primarily transmitted to people through the bite of an infected Aedes species mosquito, the same mosquitoes that spread dengue and chikungunya viruses. They typically lay eggs in and near standing water in things like buckets, bowls, animal dishes, and flower pots. They prefer to bite people rather than animals and live both indoors and outdoors near people.
Mosquitoes become infected with Zika virus when they feed on a person already infected with the virus. Infected mosquitoes can then spread the virus to other people through their bites.
The CDC and other health officials around the world believe that Zika infection during pregnancy can cause a birth defect of the brain called microcephaly and other severe fetal brain defects. The CDC also says that other problems have been detected among infants infected with Zika virus before birth, such as defects of the eye, hearing deficits and impaired growth.
There are now also reports that Zika may be associated with Guillain-Barré syndrome, an uncommon illness that affects the nervous system. Ironically, Guillain-Barré syndrome also sometimes manifests as a result of adverse vaccine reactions. One study published at the National Center for Biotechnology Information’s online library PubMed found that flu vaccines led to an estimated 1.6 additional cases of Guillain-Barré Syndrome per million vaccinations.
Army Major Leyi Lin, who is a principal investigator for the study, also noted that there are possibilities that vaccination with ZPIV or with any of the other vaccines that are aimed to prevent flavivirus infections could lead to vaccinated service members becoming even more sick if they contracted Zika virus after vaccination.
“Uniquely, illness as a result of natural infection from JE, YF or Zika could be more severe when prior flavivirus infection or vaccination exists. Our study assesses co-vaccination to learn how to reduce risk when protecting against circulating flaviviruses.”
An earlier study found that rhesus monkeys vaccinated with ZPIV developed a “strong immune response” and were protected against two strains of Zika virus, Army officials say.
The Army’s experimental Zika vaccine also will soon be part of a National Institute of Health trial that began in August for another Zika vaccine. The NIH’s Zika vaccine contains foreign DNA that instructs volunteers’ cells to make Zika proteins in order to produce an immune response. Researchers plan to give the Army’s ZPIV as a booster after they receive the NIH’s DNA vaccine, Army officials say.
Three more trials are set to begin this year testing ZPIV on other volunteers. One is designed to determine the optimal dose of the vaccine, one to study the safety and efficacy of the vaccine on a “compressed vaccine schedule,” and one will study the vaccine’s safety for people who have already been exposed to Zika virus or other flaviviruses.
[Featured Image by Brett Flashnick/AP Images]