A single-dose Zika vaccine developed by UT Medical Branch researchers is one step closer to protecting humans from the virus.

For the first time, UTMB researchers protected primates from Zika infection and symptoms with a vaccine, according to a study published in Science Communications last week.

Zika infection in pregnant women causes incomplete brain development in their babies. The virus can also damage testicles and lower sperm counts in infected males. Pei-Yong Shi, the lead researcher for the Zika vaccine, said UTMB’s vaccine created immunity in tested primates within two weeks of vaccination, preventing infection and subsequent health risks.

“What we found is a single-shot, a single dose of this (vaccine) candidate can fully protect these monkeys,” Shi said. “By having a vaccine we’ll definitely sustain and achieve the lowered infection rate.”

UTMB researchers previously tested another Zika vaccine, but it required multiple doses and more time to immunize mice and primates. The new, more successful vaccine consisted of an active Zika virus that helps the primates’ bodies build antibodies to fight the Zika virus with just one dose.

Pedro Vasconcelos, a Brazilian researcher and co-developer of the vaccine, said the quick-action single-dose vaccine would be more helpful to less advantaged populations of Latin America, where Zika became widespread in 2015. 

“Having a Zika vaccine that can protect male reproductive systems, pregnant women and their unborn babies would improve public health efforts to avoid birth defects and other effects of the disease in regions where Zika is circulating,” Vasconcelos said in a UTMB press release. “Vaccines that require booster shots are impractically challenging for people living in developing regions where access to medical facilities may be limited.”

The vaccine remains untested on humans, but Shi said the vaccine could help prevent the transmission of Zika within a year if consequent safety studies go as planned. The vaccination of pregnant women would require more extensive studies, Shi said. Now that the vaccine has been shown to confer immunity, UTMB’s researchers will conduct safety tests and focus on finding a way to mass-produce the more effective vaccine.  

“I think the ideal scenario would be to vaccinate the population before childbearing age,” Shi said.

The number of reported Zika cases has dropped since 2016 because of increased exposure to the virus and “herd immunity,” Shi said. However, there are still Zika infections and various researchers, including UT professor Sahotra Sarkar, predict that mosquitoes could bring to life another Zika epidemic sometime in the future.

“The attention to mosquitoes should remain,” Sarkar said. “The underlying mechanisms for an outbreak still exist.”

People in Latin America, Africa and regions of Asia continue to be at particular risk of Zika outbreaks because they are a breeding ground for the Aedes mosquito, which carries Zika throughout the tropics. Since researchers still cannot determine when the next outbreak could occur, Sarkar recommends monitoring and controlling mosquito populations worldwide.