Navy Dengue Vaccine Enters First Clinical Trial

By Terri Moon Cronk
American Forces Press Service

SILVER SPRING, Md., April 26, 2012 – Navy medical researchers are conducting their first human clinical trial for a vaccine to protect U.S. troops from dengue, a potentially deadly mosquito-transmitted virus found in the tropical and subtropical areas of the world.

No treatment or cure exists for dengue, which is carried by a particular type of mosquito, said Navy Cmdr. Tad Kochel, chief of Viral and Rickettsial Disease research at the Naval Medical Research Center, here. Kochel said the disease is endemic in Southeast Asia, Africa, South America and the Caribbean.

Dengue puts 2 million people at risk worldwide, and adds about 500,000 new cases each year, Kochel said. Dengue also can cause 25,000 deaths annually, mostly among children who aren’t hospitalized before severe illness can set in.

“We need a vaccine because the troops are deployed where dengue is actively transmitted,” said Kochel, who developed the Navy’s dengue vaccine in 1993, which is now in the trial phase to determine whether it is safe and effective. Kochel, who has a doctorate in virology, said a vaccine against the virus will have to cover each of its four strains.

Some dengue strains cause few symptoms, while others can cause high fever, internal bleeding and shock, among other symptoms, said Navy Lt. Cmdr. (Dr.) Janine Danko, department deputy chief.

Dengue is not contagious, she said. It is contracted when bitten by a mosquito carrying the virus. Once a person is bitten, however, subsequent bites from infected mosquitoes have cumulative effects and can result in more severe cases of the disease.

“People who get it a second or third time in their lives can have more severe disease symptoms,” Danko said. “A soldier who is deployed to a tropical area, bitten by a mosquito and infected with dengue may not even know it. He may feel ‘punky’ and have a fever a day or two. If he’s deployed again to other areas with dengue, he’s at higher risk of infection, because his body has seen it before.”

Because there is no treatment for dengue, prevention is vital.

“We always have campaigns to reduce dengue transmission,” Kochel said. “Troops in endemic areas are encouraged to kill the mosquitoes, use pesticides, ensure living areas have no standing water, and use a repellent. But these things are not 100 percent. That’s why we need a vaccine.”

Research for a dengue vaccine has been under way for more than 20 years, but its availability still is five to 10 years away, Kochel said.

A vaccine that prevents all four strains of dengue must pass stringent Food and Drug Administration requirements before it can be licensed and marketed for human use.

The price tag that comes with vaccine development also is great.
“The dollar amount for these studies is pretty exponential,” Kochel said.

The Navy researchers emphasized that they’re not working in a vacuum to develop a vaccine.

“The Navy, in collaboration with the Army, has three vaccines,” Kochel said. “We are testing products individually and in combination with our counterparts, such as universities and private companies that also are working on vaccines.”

Of the various vaccines in different stages of development, Kochel said, not one is ahead of the others.

“Everyone’s trying to get over this hurdle of getting good immune responses against all four types of the virus,” he said, adding that the “perfect vaccine” does not yet exist to protect U.S. troops from all strains.

And even though dengue’s Type 1 strain might go unnoticed in some people, the virus doesn’t have to be severe before it can be a hindrance to troop strength, Danko said.

“Even with moderate infection,” she explained, “dengue affects our ability on the front lines to protect and carry out the mission of DOD.”