Three different experimental Zika vaccines being developed in the United States have worked well in monkey studies, paving the way for human trials in the coming months, researchers said.
Consistent and robust protection
The report, published in the journal Science, comes as researchers rush to find a way to prevent the mosquito-borne virus, which can cause severe birth defects. It is currently spreading in 50 countries and territories, mainly in Latin America, the Caribbean and the US state of Florida.
"Three vaccines provided complete protection against Zika virus in non-human primates, which is the best animal model prior to starting clinical trials," said senior author Dan Barouch, professor of medicine at Harvard Medical School.
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"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 in development is called a Zika purified inactivated virus (ZPIV) vaccine, made by the Walter Reed Army Institute of Research (WRAIR).
Rhesus monkeys vaccinated with it "showed complete protection against both Brazilian and Puerto Rican strains of Zika," said the study.
Caution advised in humans
Harvard University's two candidate vaccines, one a plasmid DNA vaccine and another an adenovirus vector-based vaccine, also protected the monkeys. No adverse side effects were observed in any of the animals.
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According to Sarah Gilbert, professor of vaccinology at the University of Oxford, the research "describes an important step in the development of a Zika virus vaccine".
But Gilbert, who was not involved in the research, advised caution in proceeding with testing the vaccines in humans.
"It is known that antibodies against one serotype of the closely related dengue virus can make subsequent infections with a different serotype much more severe," she said.
"It will be necessary to make sure that people receiving a Zika vaccine do not then become more susceptible to severe dengue infections, which can be fatal."
She also noted that while all three vaccines were effective, the DNA vaccine "perform(ed) less well at inducing immune responses in monkeys".
Two other experimental vaccines currently in human trials in the US and Canada are DNA vaccines.
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