A single dose of the first live-attenuated Zika vaccine -- in which the virus has been weakened so that it cannot cause disease -- has been found to provide mice complete protection in experiments.

Rapid and promising progress has been made towards Zika vaccines, but they have been made either from an inactivated version of the Zika virus or subunits of the virus. "We chose to pursue a vaccine made from live virus that has been sufficiently attenuated, or weakened, to be safe, and is able to illicit robust immune response to protect us from Zika virus infection," said study senior author Pei-Yong Shi, Professor at the University of Texas Medical Branch at Galveston in the US.

"Such live-attenuated vaccine has the advantage of single-dose immunisation, rapid and strong immune response and potentially long-lived protection," Shi said. To create the vaccine, the researchers engineered the Zika virus by deleting one segment of the viral genome. A single immunisation with the vaccine candidate produced strong immune responses and prevented the virus from infecting mice at all, according to the study published in the journal Nature Medicine.

Shi explained that the data indicate that the vaccine the team is developing has a good balance between safety and efficacy.  "Safety is a major hurdle when developing a live-attenuated vaccine. Our Zika vaccine showed promising safety profile in mice when compared with clinically approved live-attenuated vaccines, such as the yellow fever vaccine," Shi said. The researchers believe that this vaccine will improve the public health efforts to avoid the birth defects and diseases caused by Zika in countries where the virus is commonly found. 

"The initial target of this vaccine is women of childbearing age, their sexual partners and children less than 10 years old," co-author Pedro F. C. Vasconcelos, Director of the Evandro Chagas Institute at the Ministry of Health in Brazil, said.