Aug. 16 (UPI) -- The first clinical trial of a live, weakened Zika vaccine in humans has begun, the National Institute of Allergy and Infectious Diseases announced on Thursday.
The vaccine for Zika, a disease mainly spread by mosquitoes, was developed by scientists at the NIAID, the agency announced.
NIAIA is sponsoring the trial among 28 healthy, non-pregnant adults ages 18 to 50 at the Johns Hopkins Bloomberg School of Public Health Center for Immunization Research in Baltimore, Md., and at the Vaccine Testing Center at the Larner College of Medicine at the University of Vermont in Burlington.
Twenty participants will receive the Zika vaccine and eight will get a placebo, according to ClinicalTrials.gov.
No licensed vaccines for Zika virus infection are available, although several are in development.
Inovio Pharmaceuticals has finished a clinical trial in Puerto Ruco of synthetic DNA plasmid vaccine. The results have not been announced for the synthetic vaccine, which is not made from bacterial cultures.
An attenuated vaccine is created by reducing the virulence of a pathogen, but still keeping it viable.
The virus, manufactured by Charles River Laboratories in Pennsylvania, showed promise in earlier tests in monkeys. The human trial is projected to take one year.
Zika virus is mainly transmitted to humans from an infected mosquito's bite or can be transmitted through sex.
"Zika virus infection remains a significant threat to pregnant women and their developing fetuses, and we can expect to see periodic outbreaks and cases in areas where Aedes aegypti mosquitoes thrive," Dr. Anthony S. Fauci, the NIAID director, said in a press release. "NIAID remains committed to developing safe and effective Zika vaccines, and we are pleased to begin clinical testing of a live attenuated candidate."
The Centers for Disease Control and Prevention advises pregnant women not to travel to areas with risk of Zika. In addition, the CDC recommends partners of pregnant women and couples considering pregnancy should take certain precautions.
According to the CDC's U.S. Zika Pregnancy and Infant Registry the number of pregnant women with laboratory evidence of possible Zika virus infection since 2015 includes 2,474 pregnancies in states and the District of Columbia and 4,900 in U.S. territories and freely associated states. Through July 17, the registry includes infections acquired via travel, sexual exposure or local transmission.
The experimental vaccine, known as rZIKV/D4Δ30-713, was developed in the NIAID's Laboratory of Viral Diseases and led by Dr. Stephen Whitehead.
The vaccine's virus, which is weakened, consists of a dengue virus type 4 backbone that expresses Zika virus surface proteins. Dengue is caused by any of four related viruses, termed serotypes.
Like other vaccines, when injected into the body, the weakened virus should prompt an immune response.
Whitehead also developed a dengue vaccine candidate called TV003 designed to elicit antibodies against all four dengue virus serotypes. It is being tested in a clinical trial conducted in Brazil by the Butantan Institute.
Ultimately, Whitehead plans to develop a vaccine that protects against Zika and dengue.
Dengue and Zika have been found to have circulated in at least 100 countries in Asia, the Pacific, the Americas, Africa and the Caribbean.
In 2016, Johns Hopkins launched the first known multidisciplinary Zika virus center in the world