Early analysis from the world’s first ever efficacy trial of an experimental vaccine against dengue fever shows promising results. In a study involving 4,000 children in Thailand, the vaccine appeared to prevent infection by three of the four circulating strains of the virus and showed an excellent safety profile, its French drug maker Sanofi told the press on Wednesday.

The purpose of Sanofi’s dengue vaccine is to prevent dengue disease in children and adults living in endemic areas of Asia and Latin America, and also for children and adults travelling to endemic countries, such as expatriates, military personnel, and their families.

Michel De Wilde, Executive Vice President of Research and Development at Sanofi Pasteur, the vaccines division of Sanofi, said the results of the trial “represent a key milestone in the quest to develop a safe and efficacious human vaccine against dengue”.

“This is also an important development for global public health, since there is currently no specific treatment or prevention for dengue,” he added.

The rate of dengue, a mosquito-borne infection found in tropical and sub-tropical regions, has risen dramatically around the world in recent decades, mostly in urban and semi-urban areas. It is also spreading geographically: a recent outbreak in Florida shows that dengue is now reaching continental USA outside the endemic areas of Hawaii and Puerto Rico.

There are currently 50 to 100 million people infected every year, and over 40% of the world’s population, that is over 2.5 billion people, are estimated to be at risk, says the World Health Organization (WHO).

There are four related but distinct viruses that cause dengue fever. The infection causes flu-like symptoms, and occasionally develops into hemorrhage and shock, known as severe dengue, a leading cause of serious illness and death among children in some Asian and Latin American countries.

There is currently no effective treatment for dengue fever, and the only way to control its spread at present is to control the mosquito.

The US Food and Drug Administration (FDA) has given Sanofi’s experimental dengue vaccine fast track status, meaning the federal agency recognizes such a vaccine potentially meets an important unmet need for a serious disease.

The Sanofi Pasteur dengue vaccine candidate is a live attenuated vaccine, given as 3 doses, 6 months apart (month 0, month 6, and month 12 of the trial).

The safety and efficacy trial was conducted in 4,002 children aged 4 to 11 years in Thailand, as a partnership between Sanofi Pasteur and the Mahidol University under the patronage of the Thai Ministry of Public Health in Muang district of the Ratchaburi Province.

Sanofi say the vaccine generated antibody response for all four dengue virus serotypes and early analysis of the trial results show evidence of protection against three of the four virus serotypes circulating in Thailand.

The company say they are still analysing the results to understand why the vaccine failed to protect against the fourth virus serotype “in the particular epidemiological context of Thailand”.

The most important news, they say, is the results confirm the “excellent safety profile” of the experimental vaccine.

The full data is now being reviewed by experts and public health officials, and the intention is to publish the results of the study in a peer-reviewed journal for scrutiny by the scientific community later this year.

Large scale phase III trials of the dengue vaccine are already under way. These involve 31,000 participants in 10 countries, 5 in Asia (the Philippines, Vietnam, Malaysia, Indonesia, and Thailand) and 5 in Latin America (Mexico, Colombia, Honduras, Puerto Rico and Brazil).

The studies are expected to generate important extra data about how the vaccine performs against the four circulating dengue viruses in a wider population in varied settings.

Written by Catharine Paddock PhD