There is no licensed vaccine to prevent disease caused by Zika infection, but
the NIH say the clinical trial underway for the past year has produced encouraging results.
The trial is being led by the National Institute of Allergy and Infectious Diseases, a part of the NIH that developed the vaccine. As the trial enters the next phase, the institutes say they will enroll at least 2,490 healthy participants in areas of confirmed or potential active mosquito-transmitted Zika infection.
This includes Houston and Miami in the continental United States, as well as Puerto Rico, Brazil, Peru, Costa Rica, Panama and Mexico.
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.
“All participants will receive the investigational vaccine intramuscularly at three separate clinic visits each four weeks apart,” the NIH says. “Participants will be randomly assigned to receive either a standard dose or a high dose of the investigational vaccine at all three visits, and will be followed for about 32 weeks total.”
The other 2,400 participants are needed for Part B.
“This part of the trial aims to determine if the vaccine can effectively protect against Zika-related disease when someone is naturally exposed to the virus,” according to a statement Friday from the NIH.
In addition to the same three locations from part A (Houston, Miami and San Juan), the clinical trial will operate at two additional sites in San Juan, two sites in Costa Rica, and one site each in Peru, Brazil, Panama and Mexico.
The NIH notes that it might add more sites down the line.
“Participants will be randomly assigned to receive either the investigational vaccine or a placebo at three separate clinic visits each four weeks apart,” according to the NIH statement. “The trial is double-blind, meaning neither the study investigators nor the participants will know who receives the investigational vaccine.”
Scientists will track Part B participants for nearly two years, during which time they will test for adverse events and symptoms of Zika infection.
Mild symptoms such as red eyes and a fever are common for people infected with Zika. When a Zika infection occurs during pregnancy, however, the fetus can develop a range of congenital defects.
Aside from mother to child, the virus can transmitted sexually and via the bite of infected Aedes aegypti mosquitoes.
Scientists derived the Zika vaccine platform from a strategy that was used to develop a West Nile virus vaccine candidate.
“The Zika vaccine candidate being tested in this study contains a small circular piece of DNA called a plasmid into which scientists have inserted genes that encode two proteins found on the surface of the Zika virus,” according to the NIH statement. “Once injected into muscle, the encoded proteins assemble into particles that mimic Zika virus and trigger the body’s immune system to respond. The vaccine does not contain infectious material, so it cannot cause Zika infection.”
The study is expected to be completed by 2019.