Scientists have found two potential vaccine candidates that may help combat the Zika virus. A single shot of each vaccine was shown to completely protect mice against two strains of the mosquito-borne disease, according to a new paper published in the journal Nature. These shots still need to be tested on humans, but the researchers are hopeful that either could eventually prove to be a safe and effective Zika vaccine.

"The protection was striking."

"These two vaccine candidates both provided complete protection against Zika virus challenge in mice," said study author Dan Barouch, a virologist at Beth Israel Deaconess Medical Center at Harvard Medical School. "To the best of our knowledge, this is the first report of Zika virus vaccine protection in an animal model. The protection was striking."

The two vaccines protect the body in different ways. One involves injecting specialized DNA sequences into the body, while the other works by injecting an inactive form of the Zika virus. However, both triggered the same response in mice: they caused the rodents to produce antibodies that target specific proteins in the virus. This gave the mice complete protection when exposed to a Brazilian strain and a Puerto Rican strain of Zika. The mechanism is similar to how some working vaccines combat other types of flavivirus — the family of mosquito-borne viruses that includes Zika.

The news is promising as researchers have been scrambling to find a way to combat the ongoing outbreak of Zika in Central and South America. The problem has grown so bad that the World Health Organization declared a public health emergency in the region on February 1st. Brazil, which has been hit hardest by the epidemic, reported more than 90,000 likely Zika cases between February and April of this year, according to Reuters. The country is thought to have had more than 1.5 million cases since the onset of the outbreak in April 2015, according to WHO.

The CDC concluded that Zika does indeed cause microcephaly

Meanwhile, the epidemic has also coincided with a spike in microcephaly cases — a condition in which babies are born with abnormally small heads. Growing research has shown that expectant mothers who are infected with the Zika virus early on in pregnancy are at high risk of giving birth to babies with these brain defects. And in April, the US Centers for Disease Control and Prevention (CDC) concluded that Zika does indeed cause microcephaly. For most adults, Zika only causes a fever and other minor symptoms; however, the CDC is also investigating a link between the virus and Guillain-Barré syndrome, a neurological auto-immune disease that can cause paralysis and death in people of all ages.

The vaccine candidates described in today’s study are not the only Zika vaccines being developed. This month, the US Food and Drug Administration gave the go ahead for an experimental Zika vaccine, manufactured by Inovio Pharmaceuticals, to be tested on humans. The company claimed the vaccine, called GLS-5700, produced "robust antibody and T cell responses" in animals, though Inovio did not specify if the vaccine provided complete Zika protection like these vaccines did.

But as promising as these vaccine candidates are, there are still a number of unknowns. Scientists will need to see how the vaccines work on larger animals, before moving on to human clinical trials. But given how effective the shots were in mice, Barouch is optimistic. "Clinical trials should proceed as quickly as possible," he said.

The Zika virus, explained