US health authorities on Wednesday announced the launch of a clinical trial of a vaccine to fight the Zika virus.

At least 80 volunteers between the ages of 18 and 35 are expected to participate in the trial, which is to take place at three study sites, the National Institute of Allergy and Infectious Diseases (NIAID) said.

The NIAID called the trial an "early-stage study" that would evaluate the vaccine's safety and ability to generate an immune system response in participants.

Scientists at NIAID's Vaccine Research Centre developed the vaccine against the mosquito-borne virus earlier this year, the institute said.

"A safe and effective vaccine to prevent Zika virus infection and the devastating birth defects it causes is a public health imperative," NIAID Director Anthony Fauci said.

Fauci said tests of the vaccine in animals "have been very encouraging."

He cautioned that it will take some time before a vaccine against Zika is commercially available.

The study is part of the US government response to the ongoing outbreak of Zika, which set off alarms early this year when the virus became rampant in parts of South America. The disease recently spread to Florida, with authorities saying this week that the number of confirmed mosquito-transmitted cases of Zika virus in the south-eastern state had grown to 14.

The World Health Organization (WHO) in February declared the Zika virus a public health emergency of international concern.

In the same month, the White House sought money from Congress to expand mosquito control, research into a vaccine and other programmes. After Congress failed to act, the White House said it would shift 589 million dollars to combat Zika from money previously set aside to fight Ebola.

White House spokesman Josh Earnest on Wednesday criticized the Republican-led US Congress for not approving the original request for Zika spending.

Members of Congress "left on recess a day early and told the American people 'good luck,'" he said.

The US vaccine trial announced Wednesday follow widespread mosquito eradication efforts in South America, particularly in Brazil where the summer Olympics begin Friday.

Zika infections are usually asymptomatic, but some people experience mild illness lasting about a week. In pregnant women, though, a Zika virus infection can cause a birth defect called microcephaly in the brain of the fetus and other severe fetal brain defects.

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