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By Dennis Thompson

HealthDay Reporter

WEDNESDAY, July 6, 2016 (HealthDay News) -- The French pharmaceutical firm Sanofi said Wednesday that it's joining with U.S. Army researchers to work on a vaccine for Zika virus, which has caused thousands of birth defects, primarily in Brazil.

Brazil is the site of the upcoming Summer Olympics.

Sanofi Pasteur said it will begin working with the Walter Reed Army Institute of Research (WRAIR) on development of a potential vaccine. The institute will transfer its inactivated Zika virus technology to Sanofi Pasteur, opening the door to what the drugmaker called a "broader collaboration with the U.S. government."

Sanofi said it's working on pre-clinical studies that utilize technology previously and successfully used to develop both its dengue fever and Japanese encephalitis vaccines.

"Zika, Japanese encephalitis, and dengue belong to the same family of viruses [flaviviruses], are transmitted by the same type of mosquito, and share some similarities at the genetic level, and we already licensed vaccines against those flaviviruses," John Shiver, senior vice president for research and development at Sanofi Pasteur, said in a company news release.

Last month, WRAIR researchers reported that two studies done with mice supported the potential effectiveness of two Zika vaccine candidates.

This "critical first step" will lead to trials in monkeys and humans, "and gives us early confidence that development of a protective Zika virus vaccine for humans is feasible," said researcher Col. Nelson Michael. He is co-leader of WRAIR in Silver Spring, Md., and a member of a team involved in the search for a vaccine against the mosquito-borne virus.

Zika infection during pregnancy can cause a devastating birth defect known as microcephaly, where an infant is born with an abnormally small head and brain. In Latin America, thousands of babies have already been born with microcephaly, and health officials are working to help prevent cases in the United States as the summer mosquito season arrives.

Reporting June 28 in the journal Nature, researchers said one of the new experimental vaccines was developed at Harvard Medical School in Boston and is partly based on a Zika strain isolated in Brazil.

The other vaccine, using a strain isolated in Puerto Rico, has been developed by Michael's team at WRAIR.

Both vaccines shielded mice against Zika infection with just a single shot required, the researchers said.

"We showed that vaccine-induced antibodies provided protection, similar to existing vaccines for other flaviviruses," said Dr. Dan Barouch. He directs the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston.

In related news, the U.S. National Institutes of Health (NIH) said it will study some U.S. athletes and Zika during the upcoming Summer Olympics and Paralympics in Brazil. The goal: to better understand how the virus infects people, the Associated Press reported.

Health officials have recommended that pregnant women avoid the games, which begin Aug. 5. But, the Zika virus can also be spread through sexual activity. Some athletes from several countries have already said they'll skip the games due to concerns about potential infection with Zika.

No nation has been more affected by the Zika epidemic than Brazil, where an estimated 5,000 babies have been born with microcephaly.

The NIH plans to recruit at least 1,000 athletes, coaches and staffers for its study. The participants will provide samples of bodily fluids for routine testing to help determine risk factors for infection, and how long the virus remains in the body, the AP reported.

Most people infected with Zika typically experience mild symptoms. But the risks to a pregnant woman and a fetus are very real.

To date, the vast majority of Zika infections have occurred in Latin America and the Caribbean.

So far the U.S. Centers for Disease Control and Prevention says there have been no local transmissions of Zika reported in the United States. But health officials have said they expect to see local transmission -- particularly in Gulf Coast states such as Florida, Louisiana and Texas -- as the mosquito season wears on.

Zika is typically transmitted via the bite of the Aedes aegypti mosquito. However, transmission of the virus through sex is more common than previously thought, World Health Organization officials have said.

Women of child-bearing age who live in an active Zika region should protect themselves from mosquitoes by wearing long-sleeved shirts and long pants, using mosquito repellent when outside, and staying indoors as much as possible, according to the CDC.

More information

Visit the U.S. Centers for Disease Control and Prevention for more on the Zika virus.

This Q&A will tell you what you need to know about Zika.

To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.