"In addition, NIAID is helping to develop an investigational mRNA Zika vaccine and a live-attenuated vaccine candidate created to protect against Zika and all 4 strains of dengue virus".
The researchers, who are affiliated with the National Institutes of Health, injected 45 healthy adults between the ages of 18 to 50 with the vaccine.
The investigational Zika purified inactivated virus (ZPIV) vaccine was well-tolerated and induced an immune response in participants, according to initial results from three Phase 1 clinical trials.
The second study tested two forms of a DNA-based vaccine created by NIAID scientists soon after reports surfaced linking Zika infection during pregnancy to birth defects. Neither participants nor investigators knew who received the vaccine and who received the placebo. Case counts of Zika in the USA for 2017 are 362 for US states and 594 for the territories.
The team tested two different plasmids: VRC5288 and VRC5283. The investigational vaccine was administered with an adjuvant (a compound that helps induce a stronger immune response) containing aluminum salts.
Investigators tested participants' blood samples periodically and detected antibodies to Zika virus in more than 90 percent of individuals who received the experimental vaccine, within four weeks after the last dose.
Scientists in the USA have developed an experimental Zika vaccine which has been found safe in preventing infections.
They found that one method - split-dose vaccinations by needle-free injection, which delivers a stream of fluid through the skin - was particularly effective at producing an immune response. Investigators are also working on "an experimental DNA vaccine, which is now in Phase 2 trials at sites in the United States, Central, and South America", according to the press release.
They wrote said the results from both trials are promising, but more research is needed to address key questions.
Other challenges are field efficacy testing, given Zika's pattern of rapidly emerging bursts followed by rapid decline, and the difficulty of conducting trials in nonpregnant participants with a disease that has mild symptoms.
While Zika experts have not precisely determined the concentration of antibodies needed to protect against congenital infection, animal model studies are helping to provide useful insights.
The Zika virus gained its notoriety in 2016 when a startling increase in infants born with microcephaly in Brazil was linked with infection with the virus. They noted that it took almost 30 years for a rubella vaccine to become available, and though Zika incidence has dropped in most countries, its spread has been wide and unpredictable.