Dengue vaccine offers partial protection

NEW ORLEANS — Dengue fever, a dangerous viral disease that has spread across the globe over the last 50 years, has run into an obstacle. New test results from Latin America find that an experimental vaccine aimed at all four subtypes of dengue appears to protect against the virus nearly two-thirds of the time.

Vaccination with even one dose of the three-shot course delivered substantial protection, and the vaccine limited cases of severe dengue, which can be fatal, researchers at vaccine maker Sanofi Pasteur reported November 3 at a meeting of the American Society of Tropical Medicine and Hygiene. The study also appeared online on the same day in the New England Journal of Medicine.

Some vaccines, such as those for influenza and whooping cough, also don’t provide blanket protection but help suppress the target disease. “I think we’re truly at a crossroads with dengue,” said Duane Gubler, an infectious disease researcher at Duke University and the National University of Singapore. He noted that the Sanofi vaccine is one of three in advanced stages of testing against dengue and arrives when antiviral drugs and mosquito-control technologies are also making headway. “I’m of the opinion that we’re at the beginning of a new era where we have the potential to actually impact transmission,” Gubler said. He has consulted for Sanofi but wasn’t involved in the new study.

The new Sanofi findings are somewhat better than previous tests of the dengue vaccine in Southeast Asia, which included younger children (SN: 10/20/12, p. 18). This study enrolled 20,869 children ages 9 to 16 in Brazil, Colombia, Mexico, Honduras and Puerto Rico.  By random allotment, two-thirds of the kids got dengue vaccinations, while one-third got placebo shots. The study was designed for kids to receive three shots over one year. After that, they were monitored for dengue for another 13 months.

The scientists calculated that a full three-shot course was 61 percent effective in preventing dengue. But not every child returned for all three shots. Even so, when researchers tabulated all children who got at least one shot, the protection rate was nearly 65 percent.

The vaccine was partially effective against all four dengue subtypes, which vary widely in prevalence depending on region. For example, subtype 2 was the most common one in Mexico, whereas subtype 4 was tops in Brazil. In kids getting at least one shot, the vaccine protected at a 55 percent rate against subtype 1, a 50 percent rate versus subtype 2, a 74 percent rate for subtype 3 and an 81 percent rate against subtype 4. In particular, protection against subtype 2 was better in Latin America than in the earlier study in Southeast Asia.

During the study, 12 severe cases of dengue arose. All but one showed up in children getting the placebo shots. And the one child who got severe dengue despite vaccination didn’t need hospitalization, said study coauthor Gustavo Horacio Dayan, a physician and researcher at Sanofi who presented the findings before a packed room at the meeting.  

About four-fifths of the children had had a brush with dengue beforehand, blood tests showed. Those children were better protected by the Sanofi vaccine than were unexposed kids. Stephen Thomas, a physician at Walter Reed Army Institute of Research in Silver Spring, Md., wonders whether that means people who have never encountered dengue, such as travelers, might not benefit much from the vaccine. Even so, he calls the new study a milestone in the fight against dengue. Writing November 3 in the New England Journal of Medicine, Thomas says a vaccine, even one that falls short of total effectiveness, would offer protection “and perhaps even reduce the proportion of patients with severe disease.” Side effects of the vaccine were largely mild.

Dengue virus, carried by the Aedes aegypti mosquito, has touched the southern tips of the United States (SN: 10/28/2006, p, 286). By one estimate, dengue sickens 96 million people each year worldwide.