By Robert Preidt, HealthDay Reporter

(HealthDay)

MONDAY, Dec. 23, 2019 (HealthDay News) -- An experimental Zika virus vaccine that was given before pregnancy protected monkey fetuses, researchers say.

The Zika DNA vaccine VRC5283 lowered levels of Zika virus in pregnant rhesus macaques and reduced the risk of fetal problems, according to the study published Dec. 18 in the journal Science Translational Medicine.

The vaccine is in early-stage human trials.

This study was the first to test a Zika vaccine given before conception with exposure to the virus during pregnancy, said virologist Dr. Koen Van Rompay, a scientist at the California National Primate Research Center at University of California, Davis.

Fetuses of pregnant women infected with Zika have a high risk of death, microcephaly (a smaller-than-normal head) and other abnormalities. There is no approved vaccine.

This study with monkeys was designed to resemble a real-world situation in which women could receive a Zika vaccination months or years before becoming pregnant, the researchers explained.

They said their findings could help in the development and approval of the VRC5283 vaccine for use in humans. However, results of animal testing are often different in people.

The team vaccinated female monkeys who weren't pregnant. After vaccination, they were housed with males and allowed to mate. Thirteen vaccinated females and 12 unvaccinated control animals got pregnant.

Pregnant females in both groups were exposed to Zika virus at points representing first and second trimesters.

Compared to the control group, vaccinated females had less Zika virus in their blood and it persisted for a shorter time after exposure. Two unvaccinated monkeys miscarried due to Zika infection, but there was no early fetus loss in the vaccinated group.

At the end of pregnancy, researchers examined tissues from the mothers and fetuses for Zika. Eleven of 12 fetuses in unvaccinated monkeys had detectable Zika virus in their RNA, but no Zika virus RNA was detected in the 13 fetuses from the vaccinated monkeys. Researchers said that suggests the vaccine prevented transmission of Zika to the fetus.

Antibodies against Zika in the vaccinated females correlated with protection against the virus.

The researchers are also looking into how Zika affects the development of young monkeys. "In our previous studies, we found microscopic brain lesions in fetuses exposed to Zika virus," Van Rompay said in a university news release. By observing the monkeys long after birth, his team members hope they'll learn more about how Zika affects children long-term.

The World Health Organization has more on Zika.

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