Chicago:  Mice given a single shot of one of two experimental Zika vaccines were completely protected when exposed to the virus one to two months later, a promising sign that similar vaccines under development for humans will protect against Zika, according to US researchers.

"This is an encouraging first step in Zika vaccine design and pre-clinical testing," said Professor Adrian Hill, director of Oxford University's Jenner Institute, which did not conduct the mouse study but is also developing Zika vaccines.

A natural resources officer in the US looks through a microscope at Aedes aegypti mosquitoes - the species that spreads the Zika virus. Photo: AP

Separately, US scientists said they have developed a model of the Zika virus in monkeys, a close proxy for human disease.

The studies advance efforts in fighting the mosquito-borne Zika virus, which has swept through the Americas and Caribbean, and has been linked to thousands of cases of microcephaly, as well as to neurological disorders.

On February 1, the World Health Organisation declared Zika a global health emergency.

An infant born with microcephaly in Recife, Brazil. Photo: Getty Images

"With diseases spread by biting insects, such as Zika, standard quarantine measures are useless, so stopping an outbreak in its tracks requires a vaccine-led approach," said Dr Derek Gatherer, a lecturer in the division of biomedical and life sciences at Britain's Lancaster University.

In the mouse study, published in the journal Nature, a team led by Dr Dan Barouch of Beth Israel Deaconess Medical Centre and Harvard Medical School tested two different vaccine candidates in a strain of mice that develops Zika symptoms.

Mice given either type of vaccine were 100 per cent protected from Zika after a single shot.

A container of sterile adult male mosquitos in a lab at the Mass Production Facility at the Sun Yat-Sen University-Michigan University Joint Centre of Vector Control for Tropical Disease in Guangzhou. Photo: Kevin Frayer

Unvaccinated mice that were exposed to the virus all developed symptoms of Zika.

The team also showed that antibodies taken from immunised mice could be used to protect other, unvaccinated mice, offering proof that the antibodies produced by the vaccines were specific to Zika.

"We need to be cautious about extrapolating data from a mouse model into humans," Barouch said.

Adult female mosquitos under a microscope. Photo: Kevin Frayer

But the fact that the vaccines protected mice and that their antibodies protected other mice from Zika was grounds for optimism over the development of a Zika vaccine, he said.

At least 15 companies and academic groups are racing to develop Zika vaccines, according to the WHO.

Oxford University's Hill stressed that there are still years of testing needed before a finished vaccine will be available for humans.

In another advance, researchers at the University of Wisconsin reported on Tuesday that they have successfully infected rhesus macaques with an Asian strain of the Zika virus that is currently circulating in the Americas. The study, published in the journal Nature Communications, shows that monkeys - which have immune responses similar to humans - can be used to study Zika.

Reuters