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Dengue fever, also known as breakbone fever, is a viral disease that is spread through infected mosquitoes. According to the U.S. Centers for Disease Control and Prevention (CDC), nearly 400 million people get infected every year. In order to reduce this number, researchers have been testing a new dengue fever vaccine in Asian children. So far, the trial is promising.

The trial recruited 10,275 children between the ages of two and 14 from five countries throughout Asia. The children were randomly assigned to the vaccine group or the placebo group. Children in the vaccine group received three shots, six months apart from one another. The researchers monitored the children for up to two years.

28 days after the last vaccine, the researchers reported that 117 vaccinated children developed dengue fever. The number from the placebo group was 133. The vaccine's effectiveness rate in preventing dengue fever was 56.5 percent. The team calculated that the vaccine's effectiveness rate in protecting children from acquiring the severe version of the disease was higher, at 88.5 percent.

"This vaccine has already proven to be safe," said Tyler Sharp, an epidemiologist in the dengue branch of the CDC, who was not involved with the trial, reported by Philly. "We know that this vaccine does not lead to a risk of developing severe dengue -- that is a huge step forward. [However] the 56 percent is not as high as we would like to see it. It's still a big step forward, but we have a way to go before we get a vaccine that is both safe and as efficacious as we would need it to be."

The researchers counted a total of 402 adverse side effects associated with the vaccine group. The placebo group had a total of 245 adverse events. The researchers noted that the vaccine did not protect young children as effectively as they would have hoped. Instead, the team believes that the vaccine works better as an immune booster for children who had already been exposed to the virus.

"In view of the high disease burden in endemic countries... this vaccine candidate, despite moderate overall efficacy, could have a substantial effect on public health," the researchers concluded according to Reuters.

The trial was headed by Maria Rosario Capeding from the Research Institute for Tropical Medicine in the Philippines and funded by the vaccine manufacturer, Sanofi. The study, "Clinical efficacy and safety of a novel tetravalent dengue vaccine in healthy children in Asia: a phase 3, randomized, observer-masked, placebo-controlled trial," was published in The Lancet.