Clinical Trial Results Indicate Advance in Dengue Vaccine Research

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The Dengue Vaccine Initiative (DVI) welcomes new clinical trial results that reveal progress in developing the first-ever dengue vaccine. In a publication in The Lancet, pharmaceutical company Sanofi Pasteur reported results from the first study conducted to evaluate the efficacy of any dengue vaccine candidate against clinical dengue disease in a population naturally exposed to dengue.

Dengue vaccine development efforts have been difficult because dengue is caused by four different related viruses, known as DENV 1, 2, 3 and 4. The results published in today's study found that Sanofi's vaccine candidate was effective against DENV 1, 3 and 4, but DENV 2 appeared to be resistant to vaccine in this trial. The vaccine candidate, called CYD-TDV, was tested on a group of 4,002 schoolchildren in Thailand, where dengue is known to be endemic.

"While there is still much work to be done, these clinical trials mark a decisive step forward in the development of a safe and effective vaccine," says Dr. Luiz da Silva, director of the Dengue Vaccine Initiative. "We support the progress made by Sanofi Pasteur as well as efforts by other organizations to deliver a vaccine to populations in endemic countries."

There is no vaccine available to treat or prevent dengue fever. While vaccines have been under development since the 1940s, little progress had been made until recently. Reported dengue cases have increased from an annual average of fewer than 300,000 cases during the 1980s to nearly 1 million per annum from 2000 to 2005.The WHO estimates that there are 50 million to 100 million dengue infections a year.

"This is a dramatic increase in dengue incidence rates, and yet it's very likely that the numbers still do not reflect the full scope of the problem," says Dr. Ciro de Quadros, executive vice president of the Sabin Vaccine Institute. "An exact number is difficult to determine due to a lack of accurate diagnostic testing and common misdiagnosis."

Dengue is the most common mosquito-borne viral disease, with more than 2.5 billion people at risk for the disease globally, resulting in an estimated 21,000 deaths per year. Dengue symptoms can range from mild, flu-like symptoms to severe circulatory failure, coma and death. Most outbreaks occur during the rainy season in endemic countries like Thailand and Brazil, when mosquito populations are high.

Currently, there are several dengue vaccines in various stages of development, with four candidates, including Sanofi Pasteur's, in clinical trial stages. The results of this first study, a phase IIb clinical trial, are not yet sufficient to prove or disprove efficacy of CYD-TDV. However, Sanofi has already begun phase III studies among 31,000 children in Asia and Latin America. These studies will provide further information, including pivotal efficacy results and additional safety data.

"In addition to saving lives and reducing illness, a dengue fever vaccine, once introduced, will have significant positive impacts on the global economy," adds Dr. Orin Levine, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health. "The cost of dengue fever in the Americas alone is estimated to be $2.1 billion annually, and the burden of lost wages and productivity, along with the cost of healthcare, takes a great toll in endemic countries across the globe."

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