Developments in the search for a Zika vaccine - success in mice and a new platform for flavivirus vaccines

By Sally Robertson, B.Sc.Dec 12 2019

Researchers at the University of Adelaide in Australia have created a vaccine that has proved successful at protecting mice against the Zika virus. Meanwhile, researchers at the University of Queensland have discovered a new platform for developing flavivirus tests and vaccines in the form of an insect-specific virus.

Image Credit: Kateryna Kon / Shutterstock.com

These are important developments since, currently, there is no approved vaccine available to protect people from the disease. The mouse experiment has not yet been replicated in humans, but the researchers say the vaccine shows early signs of promise.

In February 2016, the World Health Organization declared the Zika epidemic an emergency; the virus, which was first detected in Brazil, had spread to 60 countries and been sexually transmitted in six of them.

The emergency prompted scientists around the world to find a way to combat the virus, but no vaccine has yet been developed.

However, these developments are promising.

About the Zika virus

The Zika virus, which is transmitted to humans via infected mosquitoes, often causes no symptoms. However, it can cause congenital disabilities and the rare neurological disorder Guillain-Barré Syndrome, which can cause paralysis in adults. The virus can also be sexually transmitted between people, even if they are asymptomatic.

On contracting Zika, antibodies target the virus by attacking the envelope that protects it from our immune response. Many trials of vaccines have targeted this envelope, but some studies have shown that this can make people more susceptible to similar viral diseases.

Grubor-Bauk and colleagues, therefore, tried a new approach. They developed a vaccine that uses genetically engineered DNA to trigger an immune response that neutralizes the virus. This type of vaccine has demonstrated the potential to ward off various types of flavivirus, the family of viruses that Zika belongs to.

The vaccine protected mice against Zika

As reported in the journal Science Advances, when the team injected the vaccine into young albino mice three times over the course of several weeks, it generated a strong immune response that protected the animals against the virus.

Animal models are often used to test preliminary versions of drugs and vaccines, many of which fail to be effective once tested in humans. Bauk and colleagues will, therefore, need to do a lot more work before they can deliver a safe and effective vaccine to people.

However, the current development represents an important step forward in the search for a way to protect the global population from Zika. According to the researchers, the vaccine "could be easily manufactured on a large scale at low cost” and would also be "safe for children and women of reproductive age."

A new platform for vaccine development

Meanwhile, researchers at the University of Queensland may have found a way to accelerate vaccine development. They have developed a new technology that produces a safer insect-specific “hybrid” virus that can house genes from related viruses such as Zika.

The new recombinant platform serves as a flexible and non-infectious tool for investigating vaccines for various mosquito-borne diseases such as Zika, yellow fever, and dengue. So far, the development of vaccines for these diseases has been challenging because it involves using infectious strains that pose a risk to people.

Now, the University of Queensland team has exploited the benign characteristics of the Binjari virus, which is inert to humans, to create viruses such as Zika that cannot grow in humans or animals.

Jody Hobson-Peters said the team, which was led by Roy Hall, started investigating the approach after they discovered new viruses in the laboratory.

We were originally hoping to gain insights into how mosquito-borne viral diseases evolve—viruses like Zika, yellow fever and dengue. We were also hoping to discover new viruses that might be useful for biotechnology or as biological control agents.”

Judy Hobson-Peters, University of Queensland

The Binjari virus “stood out”

Hobson-Peters says the Binjari virus “stood out.” Very high volumes can be grown in mosquito cells, whilst it remains completely harmless and non-infectious to people and other vertebrates. It is also extremely tolerant of genetic manipulation, meaning researchers can take genes from viruses such as Zika and insert them into the Binjari genome.

"This produces hybrid, or chimeric, viruses that physically appeared identical to the disease-causing viruses under the electron microscope, but were still unable to grow in human or animal cells," says Hobson-Peters.

This means the researchers have effectively developed a new biotechnology platform that requires little biocontainment, to help safely develop vaccines and diagnostics for human application.

"These hybrids cannot infect humans, meaning that manufacture of vaccines and diagnostic reagents don't require the strict and expensive biosecurity infrastructure ordinarily needed to grow these pathogenic viruses,” says co-researcher Andreas Suhrbier.

It's a technology that will truly revolutionize the manufacture of vaccines—supercharging high-volume vaccine development.”

Andreas Suhrbier, QIMR Berghofer Medical Research Institute