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One-Dose Zika Vaccine Protects Laboratory Animals

FILE - A woman stands near a poster explaining the Zika virus at the Ministry of Health office in Jakarta, Indonesia, Sept. 2, 2016.
FILE - A woman stands near a poster explaining the Zika virus at the Ministry of Health office in Jakarta, Indonesia, Sept. 2, 2016.

An experimental Zika vaccine has been shown to be 100 percent effective in protecting laboratory animals from the virus, according to researchers from the Perelman School of Medicine at the University of Pennsylvania.

Scientists say one dose of the vaccine prevents transmission of the Zika virus in the animals tested, and it appears to be a potentially powerful weapon in the global war against Zika.

Messenger RNA delivers

The so-called mRNA vaccine uses genetic material from the Zika virus to protect against the mosquito-borne illness. It stands for messenger RNA, which in the body translates DNA, the blueprint for life, into proteins that carry out various biological functions.

The mRNA vaccine is different from others that stimulate the immune system by using weakened or killed pathogens.

Drew Weissman is an mRNA vaccinologist at the University of Pennsylvania School of Medicine. He developed the vaccine in collaboration with researchers at a number of institutions.

Weissman and colleagues modified tiny strands of viral RNA that hold the genetic codes for making Zika viral proteins. While RNA that’s simply injected into the body may be recognized as foreign by the immune system and swept away, the scientists developed a delivery system for the mRNA vaccine that allows it to slip unnoticed into cells, where the genetic machinery quietly makes viral proteins.

These harmless proteins enhance the immune system, so it is primed to recognize and destroy a Zika infection, if one is encountered.

One dose may be enough

Weissman says everyone would be vaccinated against the virus in areas where Zika is endemic.

A single shot of the vaccine protected mice and macaque monkeys for an extended period of time in an environment where they were exposed to Zika, Weissman said.

“What we saw when we looked at both mice and macaques is that we could give a single dose — and very low dose — of modified RNA and get complete protection,” he said. “And in mice we looked out to five months, and the protection remained potent at five months after a single immunization.”

In monkeys, the vaccine has only been observed for five weeks, but the protection seems to be holding.

The study was published in the journal Nature.

Weissman’s vaccine was made from a Zika virus strain isolated in a 2013 outbreak. The mosquito-borne illness has hit the hardest in Latin America, causing birth defects in the babies of pregnant women.

“So I think the great advantage is that unlike other vaccines described so far,” Weissman said, “you could go into a country or a region and give a single immunization and be done. So it doesn’t require any infrastructure to track down people that didn’t receive a second immunization. It doesn’t require a second immunization, so it’s going to be much easier and cheaper to vaccinate a large area.”

Weissman hopes to begin clinical trials of the mRNA vaccine within 18 months.