New Dengue Vaccine Looks Promising, but Major Hurdles Remain

A new vaccine could protect patients against dengue, but experts warn it’s not a sure bet quite yet. The preliminary results of a multi-country trial are looking promising: the vaccine was 80.2 percent effective, according to a study published in the New England Journal of Medicine.

Dengue is a mosquito-borne illness that infects nearly 400 million people each year. Most cases are either asymptomatic or result in flu-like symptoms, but some cases are severe. Those severe cases can be deadly. This year, the World Health Organization listed dengue as one of the top 10 threats to global health, and there are 30 times as many infections now than there were 40 years ago, reports NPR’s Jason Beaubien.

At that rate, it’s the fastest spreading mosquito-borne viral disease in the world, as Derek Wallace, who leads Takeda Pharmaceutical Company’s dengue vaccine program, tells NPR.

"Dengue is a very important disease across a large part of the world. Nearly half the world's population is at risk of dengue,” Wallace says.

In this most recent live vaccine trial, 20,000 children between 4 to 16 years old in eight countries across South America and Asia were given either the dengue vaccine or a placebo. A year after getting the second dose of the shot, researchers compared rates of dengue infection between children who got the placebo and those that got the vaccine, reports Science Magazine’s Jon Cohen.

They tested the vaccine’s efficacy against all four different strains, or serotypes, of the virus. The rate of infections in participants dropped 97.7 percent for the dengue 2 serotype. For the other serotypes the rate was significantly lower, 73.7 percent in the first serotype and 62.6 percent in the second. The fourth serotype wasn’t present in enough cases to get conclusive results. Further, the study found the vaccine reduced hospitalizations of people infected by 95.4 percent.

Currently, doctors can’t do much about dengue. There isn’t a vaccine or a specific treatment for the disease, so clinicians are left to treat the symptoms. That leaves researchers and others in the medical field hopeful about the new study.

"We're thrilled with the results," Wallace tells NPR.

Researchers aren’t in the clear yet and the trial is still ongoing. Takeda plans to study patients for 4.5 years after they get their last dose of the shot.

But the shadow of a previous dengue vaccine, Dengvaxia by pharmaceutical company Sanofi, looms over this evidence. It took three years of clinical trials to sort out issues in that vaccine, which had already been given to a million children in the Philippines before the program ended amid scandal. Dengvaxia was eventually found to increase the risk of dengue in people who had not already been infected, reports Ed Silverman for STAT News.

At the American Society of Tropical Medicine & Hygiene annual meeting on November 23, Takeda will share results from 18 months after the last vaccination, reports Science’s Cohen. Wallace says the new data is consistent with the findings reported this week.

The Takeda study is still “very much a preliminary report,” retired dengue expert Scott Halstead tells STAT News. Halstead, who served on a Takeda advisory board, published research warning of issues with Dengvaxia.

“This suggests victory, but Takeda recognizes this is something they’re going to have to stick with, think about, work on, watch and be careful,” says Halstead.