Researchers from the Walter Reed Army Institute of Research (WRAIR), Harvard Medical School and Beth Israel Deaconess Medical Center successfully tested two promising Zika virus vaccine candidates on mice. The team plans to begin human clinical trials before the end of the year, with more additional tests planned in the US.

One is a Harvard-developed DNA vaccine based on an isolated strain of the virus in Brazil. The other is a purified inactivated virus (PIV) vaccine isolated in Puerto Rico, which was developed at WRAIR.

“This critical first step has informed our ongoing work in non-human primates and gives us early confidence that development of a protective Zika virus vaccine for humans is feasible,” says WRAIR Zika program’s co-lead researcher, Nelson Michael.

zika virus

Aedes aegypti, Zika’s primary vector. Credit: University of Wisconsin–Madison

As reported by the study published on June 28 in the journal Nature, both vaccines produced an antibody response in mice. The two were found to be effective and safe, although the DNA vaccine only protected the animals by producing an antibody response.

Researchers at WRAIR are advancing their PIV vaccine because it is a type of vaccine that has been studied and licensed before, explains WRAIR’s co-lead researcher Stephen Thomas. The PIV vaccine is also known as ZPIV.

“Our laboratory in Thailand has been conducting biosurveillance for Zika for the past three years, since we started to observe dengue-like illnesses in Thailand and the Philippines that were not dengue and did not test positive for other likely causes,” adds Thomas, who is also a vaccinologist. “These efforts gave us a head-start for our vaccine development efforts.”

Thomas states their vaccine would decrease the risk associated with newer types of untested vaccines, which could also take some time to be licensed.  WRAIR already created other flavivirus vaccines this way before.

The PIV vaccine is expected to be tested on humans at WRAIR’s clinic in Silver Spring, Maryland, USA. The National Institute of Allergy and Infectious Diseases (NIAID) will also conduct additional human trials in the US through its Vaccine and Treatment Evaluation Units.

WRAIR is the biggest biomedical research institution directed by the U.S. Department of Defense. For more than 50 years, the research facility has been studying flaviviruses, which include the Zika virus, dengue virus and Japanese encephalitis and West Nile viruses.