A new study reveals an experimental Zika vaccine could decrease how much virus is in pregnant rhesus macaques and improve fetal outcomes.
According to California National Primate Research Center virologist Koen Van Rompay, this work could lead to the creation and approval of an experimental Zika DNA vaccine – VRC5283 – which is presently in the early human trials stage. The study, which was published in the Science Translational Medicine journal, notes that it’s the first Zika vaccine test given before conception to protect a woman if she becomes exposed to the virus while pregnant.
Pregnant women who are diagnosed with the Zika virus may have children born with major fetal defects, various abnormalities and fetal death. All these have been classified as congenital Zika syndrome.
Researchers created a study that simulated a real-world situation in which women could get vaccinated for months or years before getting pregnant. They vaccinated female monkeys with the VRC5283 vaccine based on their reproductive cycles. The female monkeys were then housed with the males in order for them to procreate. Of them, 13 vaccinated monkeys and 12 unvaccinated ones got pregnant.
The pregnant monkeys were then exposed to the Zika virus at various points of their first and second trimesters. They found that the vaccinated females did not have as much Zika in the blood and the virus suffered for a short time at the exposure. Two of the unvaccinated females miscarried because of the infection with no fetal deaths in the group that was vaccinated.
Before the monkeys gave birth, the researchers searched the tissues of both the mothers and fetuses for the Zika virus. 11 of the 12 unvaccinated group had detectable levels of Zika virus RNA. There were none in the vaccinated group, which means the vaccine kept the virus from being transmitted to the baby. Zika virus antibodies in their mothers meant the babies were protected from the infection.
What About Defects?
According to the results, it would mean the VRC5283 could keep mothers from transmitting the Zika virus to their babies, which could eventually be a possibility for humans as well. Currently, the vaccine is in the global IIb trial phase, which is being carried out by the Vaccinate Research Center at the National Institute of Allergy and Infectious Diseases to determine how safe and effective in humans it would be.
Additional research and clinical trials are necessary to determine who effective the vaccine is and get licensing for it. However, as noted in the results of the animal studies, there is support to approve the vaccine.
There is still work being done to determine if the animal model of the Zika virus. One such work is looking at how the passive antibody protects the baby from the Zika infection. Since it can take weeks for the virus antibodies to be detected, passive antibody transfers may be necessary to treat pregnant women right away.
Researchers are looking at how the virus affects the young monkeys’ development. In Rhesus macaques, there is no head malformation as noted in human infants, but one such researcher said that might actually be a rare complication. According to scientists, many infants exposed to the Zika virus before they are born may have other subtle developmental defects.
Van Rompay said other studies show microscopic lesions on the brain of those fetuses exposed to the virus. The hope is to continue watching these monkeys after giving birth will lead to other problems the virus poses in children.