A single dose of either of two experimental Zika vaccines fully protected mice challenged with Zika virus four or eight weeks after receiving the inoculations. The research, conducted by investigators supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, suggests that similar vaccines for people could be similarly protective.

Zika virus infection during pregnancy can result in microcephaly and other serious birth defects in the fetus, making the development of a safe and effective vaccine a global health priority. Scientists led by Dan H. Barouch, M.D., Ph.D., at Beth Israel Deaconess Medical Center (BIDMC) and Harvard Medical School, as well as the Ragon Institute of MGH, MIT and Harvard, developed one of the Zika vaccines. Called a DNA vaccine, it contains genetic snippets from a Zika virus strain that circulated recently in Brazil to elicit immune responses. The second vaccine is made from a purified, inactivated Zika virus that recently circulated in Puerto Rico. It was developed by Stephen J. Thomas, M.D, Kenneth H. Eckels, Ph.D., Nelson L. Michael, M.D., Ph.D., and colleagues at Walter Reed Army Institute of Research, Silver Spring, Maryland.

In a first set of mouse experiments, the BIDMC investigators established that virus-specific antibodies were induced by the DNA vaccine. Next, the teams injected either of the two experimental vaccines into additional groups of mice. Four weeks later, mice that had received the DNA vaccine were exposed to the Brazilian strain of Zika virus known to cause fetal birth defects in mice analogous to those seen following fetal Zika infection in humans. No virus replication was detected in any of the vaccinated mice. Other mice receiving the DNA vaccine were exposed to virus eight weeks later. They, too, were protected from infection. The inactivated virus vaccine also protected mice from Zika infection. Moreover, the Zika-specific antibody levels detected in the mice appeared to correlate with protection against infection.

The researchers note that both DNA and inactivated virus vaccines have been developed to prevent infection by West Nile, dengue and tick-borne encephalitis viruses, all of which are in the same virus family as Zika. "Taken together, our findings provide substantial optimism that the development of a safe and effective Zika vaccine for humans will likely be feasible," they write.