Zika vaccine demonstrates effectiveness at preventing the virus

Zika vaccine
© iStock/narvikk

A groundbreaking Zika vaccine has been proven to prevent the Zika virus effectively in preclinical animal studies.

The novel Zika vaccine was developed at the Walter Reed Institute of Research (WRAIR), in collaboration with the Trudeau Institute and Texas Biomedical Research Institute’s Southwest National Primate Research Center (SNPRC). In their research, the Zika vaccine stopped the virus from spreading from mother to foetus.

In-Jeong Kim, PhD, a viral immunologist at Trudeau Institute and the first paper author, said: “The vaccine has been shown to be safe for non-pregnant humans, but of course, we need to know if it is safe and effective for the people at greatest risk: pregnant women and their foetuses. Our proof-of-concept studies conducted at Trudeau and Texas Biomed show very promising results that the vaccine given before pregnancy will provide high levels of protection for mothers and babies.”

The study findings are published in the journal npj Vaccines.

Combatting outbreaks

Brazil and several other South American countries were devastated by the 2015-2016 outbreak of the Zika virus, resulting in a surge of miscarriages and congenital disabilities – called congenital Zika syndrome, including abnormally small heads and neurodevelopmental disorders. This led the World Health Organization (WHO) to declare the Zika outbreak as a public threat emergency of international concern.

Jean Patterson, PhD, a virologist at Texas Biomed and a senior paper author, commented: “It’s important to test vaccines before the next large outbreak because there will be another. Zika is part of a family of viruses known to go through cycles. These viruses tend to spread rapidly through naïve populations that have never been exposed to the virus before; then, infections drop down for years because most people have been exposed. As more and more people are born, there is a new group of naïve individuals in which the virus can once again wreak havoc. We want to help break that cycle.”

Zika vaccine development

The team developed its purified, inactivated Zika vaccine (ZPIV) by employing the same technology used to make a Japanese encephalitis vaccine, and it has been shown to clear the virus from the blood in non-pregnant animals effectively. Moreover, it is demonstrated to be safe and elicit a protective immune response in Phase 1 human trials.

However, due to ethical and safety reasons, the team could not perform rigorous tests to prove the Zika vaccine safeguards pregnant women and their foetuses from infection and severe malformations. Nevertheless, the researchers evaluated the vaccine in pregnant mice and marmosets, where it prevented 80% of foetal malformations and antibodies capable of neutralising the virus were detected in foetal blood samples eight days following infection.

“We were able to detect maternal antibodies in the foetus during pregnancy, and the results suggest the antibodies play a critical role in protecting foetuses from Zika virus,” Kim said.

Marmosets are more sensitive to the Zika virus than other non-human primates, with prior investigations showing that foetuses were aborted within two weeks of maternal infection. In contrast, in the study, four marmosets were administered the Zika vaccine before becoming pregnant and then were exposed to the Zika virus, with only one of their 12 offspring testing positive, showing over 90% effectiveness.

Patterson said: “Because the animals became pregnant at different times, our study was able to show the vaccine confers protection for at least 18 months after vaccination, which is important for showing long-lasting immunity.”

The team are now looking to investigate what happens when the Zika vaccine is administered during pregnancy in marmosets.

Kayvon Modjarrad, MD, PhD, who leads the US Army Zika vaccine programme and is the Director of the Emerging Infectious Diseases Branch at WRAIR, said: “These studies add to evidence that the Zika vaccine WRAIR developed not only protects animals against Zika virus infection, but also the congenital defects that mimic what has been observed in people. Together with the early phase clinical trials, we believe these data lend even more support that this vaccine platform is a viable approach for countering the persistent threat of Zika.”

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