Feb. 15 (UPI) -- A vaccine against Zika produced immunity to the mosquito-borne virus for up to a year in at least 80% of those who received it, a study published Monday by the Annals of Internal Medicine found.
People given the vaccine as part of the Phase I trial, the first step in the research and development process before U.S. Food and Drug Administration approval, experienced minimal side effects, the researchers said.
A Phase 2 trial of the vaccine is already underway, according to its manufacturer, Johnson & Johnson-Janssen.
The vaccine is part of the company's AdVac platform, which is also being used to develop and manufacture shots against COVID-19, Ebola and HIV.
Zika is spread to humans who are bitten by infected mosquitos, as well as through sexual contact, according to the U.S. Centers for Disease Control and Prevention.
The most recent outbreak of the virus occurred in 2015-16, when more than 700,000 cases were reported in the Americas, including more than 200,000 in Brazil alone, per CDC estimates.
No new cases have been reported in the continental United States since May 2019, but the disease is considered endemic in Puerto Rico, where about 100 cases are identified annually, according to the World Health Organization.
In addition, geographic expansion of the territory for the Aedes aegypti mosquito, which spreads the virus, to areas where population-level immunity is low poses a substantial risk for future epidemics, the authors of the new study said.
The virus generally causes mild, flu-like symptoms, but if pregnant women get infected, their babies are at increased risk for birth defects, including encephalitis, a brain disease.
For this study, researchers from Netherlands-based Janssen Vaccines and Prevention and Beth Israel Deaconess Medical Center in Boston randomly assigned 100 healthy participants to either a one- or two-dose regimen of the vaccine or placebo to assess safety and effectiveness.
Both dosing regimens were safe, causing only mild to moderate injection-site reactions, the researchers said.
In addition, both dosing regimens induced persistent neutralizing antibody responses, meaning they prompted the immune system of recipients to produce cells that were able to successfully fight off the virus, they said.
These antibody responses were found in at least 80% of participants who received two doses one year later.
A single-dose vaccine produced lower, but likely still effective, antibody responses, the researchers said.