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WASHINGTON, Aug. 5 (Xinhua) -- Three new experimental Zika vaccines under development in the United States have been found to be "strikingly" effective at protecting monkeys from the mosquito-borne virus, a new study has found.
Zika infections often begin with a headache. Within a few days patients may develop a rash, bloodshot eyes, and run a fever. Some patients may also develop joint pains in their wrists, knees, and ankles, as well as muscle pain, and pain behind the eyes.
While similar vaccines have been tested in mice, monkeys are a much better model to determine how vaccines will work in humans, according to the study published Friday in the U.S. journal Science.
"Three vaccines provided complete protection against Zika virus in nonhuman primates, which is the best animal model prior to starting clinical trials," senior author Dan Barouch of Beth Israel Deaconess Medical Center said in a statement.
"The consistent and robust protection against Zika virus in both rodents and primates fuels our optimism about the development of a safe and effective Zika vaccine for humans."
One of the vaccines was made with a traditional approach known as a purified inactivated virus (PIV) vaccine, which contained an inactivated copy of Zika.
The other two used newer approaches, known as a plasmid DNA vaccine and an adenovirus vector-based vaccine, respectively.
To test the PIV vaccine, scientists immunized eight rhesus monkeys with inactivated Zika virus and eight monkeys with a sham vaccine.
Within two weeks, the animals' immune systems produced antibodies against the virus, which were substantially boosted following a second shot at four weeks.
When these animals were exposed to two strains of infectious Zika virus from Brazil and Puerto Rico, they showed complete protection against the virus, with no detectable Zika virus in the blood or other bodily secretions.
The researchers said the PIV vaccine, developed by the Walter Reed Army Institute of Research could begin human clinical trial later this year.
In a second experiment, 12 rhesus monkeys were immunized with either a DNA vaccine or an adenovirus vector-based vaccine.
Both vaccines were found to produce Zika-specific antibodies in all primates tested, with the adenovirus vector-based vaccine provoking a broader and a more potent antibody response.
When the primates were exposed to the Brazilian strain of Zika virus, both vaccines provided complete protection.
Earlies this week, the U.S. National Institutes of Health announced it has launched a clinical trial of a Zika DNA vaccine in humans aimed at evaluating its safety and ability to generate an immune system response.
So far, there are no vaccines or specific therapeutics to prevent or treat Zika virus disease.
