Experimental dengue vaccine 100 percent effective in small trial

U.S. scientists said Wednesday they have made a big step towards developing an effective single-dose dengue vaccine.

In a controlled human challenge study, an experimental dengue vaccine can fully protect healthy volunteers who were intentionally infected with a weak form of the dengue virus, they reported in the U.S. journal Science Translational Medicine.

The human challenge test, said the study, could serve as an early check for dengue vaccine candidates, before launching costly and often risky large-scale trials in dengue-endemic areas, thus helping speed up vaccine development.

Dengue is the most common mosquito-borne viral infection in the world, infecting 390 million people annually. While the virus usually causes no symptoms or only mild fever, more than two million each year develop life-threatening dengue shock syndrome.

Several dengue vaccine candidates are under development, but there are currently no licensed ones that get widespread use.

One of the biggest hurdles is that fact that a dengue vaccine must protect against all four serotypes of the dengue virus to be effective, because people previously infected with one serotype are likely to get sicker if they are infected with another serotype.

In the new study, researchers from the U.S. National Institutes of Health (NIH) created the candidate vaccine called TV003 using a mixture of four live, weakened viruses targeted to each of the four dengue serotypes.

A total of 48 healthy adult volunteers enrolled at two trial sites, the University of Vermont College of Medicine and Johns Hopkins Bloomberg School of Public Health, and were randomly assigned to receive either vaccine or placebo injection.

Six months later, 41 people returned for the challenge with a weakened strain of the dengue virus that causes infection, but no or minimal symptoms.

While all 20 placebo recipients developed mild symptoms like rash and low white blood cell count, all 21 vaccinated individuals were completely protected from infection, the researchers said.

"We were well on our way to having a tetravalent dengue vaccine that produced antibodies to all four dengue serotypes after just a single dose," Stephen Whitehead, a senior scientist at the NIH, told reporters at a telephone press conference.

"It was safe, it elicited antibodies and other immune effectors, and we were confident that it could be manufactured inexpensively and could be made accessible to those who needed it most."

Whitehead also said several commercial vaccine companies from the U.S. and India showed a strong interest in acquiring the vaccine for further development.

Meanwhile, researchers in Brazil began administering the new single-dose vaccine in a large Phase three clinical trial designed to look at vaccine efficacy against naturally occurring dengue in February.

Associate Prof. Anna Durbin, who led the clinical trial at Johns Hopkins, said the methods used in this study could be the basis for developing a vaccine against other flaviviruses, including the Zika virus that is circulating in the Americas.

"We think that this is a tool that can really accelerate vaccine development," Durbin said at the same press conference. "There's an urgent need for a Zika vaccine. We are looking at strategies to really accelerate that timeline and we think that a Zika human challenge model could be very useful in that endeavor." Endit