Zika Vaccine Candidate Successfully Protects Mouse Models from Infection

Researchers from The University of Texas Medical Branch at Galveston (UTMB) and from Instituto Evandro Chagas (IEC) in Brazil may change how we approach the Zika virus.

The Zika virus has been circulating in South America since 2015, and in the United States since last year. Recently, the Texas Department of State Health Services updated its testing recommendations for six counties that are at an increased risk of active Zika transmission. A Zika infection can cause serious complications for pregnant women and their developing fetuses. Unfortunately, there has yet to be a vaccine for the mosquito-borne virus, and so, the Centers for Disease Control and Prevention recommends several precautionary measures to avoid being bitten by an infected mosquito. However, in an exclusive interview with Contagion®, Annelies Wilder-Smith, MD, PhD, professor at Lee Kong Chian School of Medicine in Singapore, said, “Of course, you can reduce landing and biting rates with personal protection, like spraying [mosquito repellant] and [wearing] long-sleeves. But we have not seen any data [saying] that good personal protection, indeed, also translates to less disease.”

So, how do we ensure that individuals are protected against infection with the Zika virus? Researchers from UTMB and IEC are collaborating on the first live-attenuated vaccine that “completely protected mice against the virus after a single vaccination dose.” Although the vaccine is still being developed, the group’s most recent findings were published in the journal Nature Medicine on April 10, 2017.

In a press release, senior author of the study, and I.H. Kempner professor at the Department of Biochemistry and Microbiology, Pei-Yong Shi, PhD, said, "A successful vaccine requires a fine balance between efficacy and safety— vaccines made from attenuated live viruses generally offer fast and durable immunity, but sometimes with the trade-off of reduced safety, whereas inactivated and subunit viruses often provide enhanced safety but may require several doses initially and periodic boosters. Therefore, a safe live-attenuated vaccine will be ideal in prevention of Zika virus infection, especially in developing countries."

The vaccine was developed using a similar approach to the one used to create an existing Dengue vaccine: the researchers used a virus candidate with a “10-neucleotide deletion in the 3’ untranslated region of the [Zika virus] genome.” The live, weakened virus is still able to elicit ample immune response that would protect against infection. The virus was found to be “protective in type 1 interferon receptor-deficient A129 mice.” These mice went on to develop “robust T-cell response.”

According to the study, the researchers believe that “decreased viral RNA synthesis and increased sensitivity to type-1-interferon inhibition” may be contributing factors to the genetically engineered virus’s low virulence.

The authors concluded, “The attenuated 10-del ZIKV was incapable of infecting mosquitoes after oral feeding of spiked-blood meals, representing an additional safety feature. Collectively, the safety and efficacy results suggest that further development of this promising, live attenuated ZIKV vaccine candidate is warranted.”

Adriano de Bernardi Schneider, MS, PhD candidate, Department of Bioinformatics and Genomics, University of North Carolina at Charlotte, said to Contagion^®, “I am happy to see the advancements in vaccines against Zika. Pedro Vasconcelos, MD, PhD, director of Instituto Evandro Chagas, mentioned to me at the First International Conference on Zika Virus that the IEC was working on this vaccine. I do believe that this vaccine has the potential to prevent future outbreaks from happening. On the other hand, with regards to current outbreaks, until we have this vaccine ready to be deployed (which will take a lot of time and money), we will have to continue looking at other ways to contain the spread of the virus, which should focus mainly on vector control and the screening of multiple safe, and available drugs that could be repurposed to treat those patients affected by Zika.”