Two experimental vaccines administered prior to pregnancy can protect vulnerable fetuses from the Zika virus infection and resulting injury, a new study in mice said Thursday.
Experiments using mice engineered to mimic human Zika infection showed that females injected with the vaccines before pregnancy and infected with Zika while pregnant bear pups who show no trace of the virus, according to the study published in the U.S. journal Cell.
"While several of these vaccine candidates have advanced to phase one clinical trials in humans, no study has established vaccine protection in the context of pregnancy," said the study, co-led by researchers from the University of Texas, Washington University and the U.S. National Institutes of Health (NIH).
The researchers tested a live-attenuated vaccine developed by the University of Texa and a mRNA or gene-based vaccine developed by Valera, a venture of the biotechnology company Moderna.
They gave groups of 18 to 20 non-pregnant female mice one injection of one of the vaccines or a placebo, and some animals received a second injection of the same vaccine or placebo a month later.
Subsequent tests revealed that mice that received mRNA vaccine or live-attenuated vaccine produced high levels of neutralizing antibodies against Zika virus in their blood.
After the mice became pregnant, they were infected on the sixth day of pregnancy, to mimic the experience of a woman bitten by a Zika-carrying mosquito early in pregnancy.
One week after infection, the scientists observed that most fetuses in the vaccinated mice showed no evidence of having Zika virus transmitted to them from their pregnant mothers.
Vaccinated mice had markedly diminished levels of Zika virus RNA in maternal, placental and fetal tissues compared to placebo-injected mice, resulting in protection against placental damage and fetal demise.
"In summary, the modified mRNA and live-attenuated vaccine platforms generated sufficient immunity to protect against infection and disease in pregnant and non-pregnant mice," the study wrote.
"Based on these data, we believe their further evaluation to prevent congenital (Zika virus) syndrome in humans is warranted."
Although the Zika virus usually does not cause significant illness in children or adults, it can cause serious birth defects when an infected pregnant woman transmits it to her fetus.
Currently, no vaccine or treatment is available to prevent or treat Zika virus disease or congenital Zika syndrome in humans.