Thailand's dengue vaccine trials show promise

By Peter Janssen Jun 20, 2011, 3:06 GMT

Bangkok - The world's first dengue vaccine is on the horizon, after decades of failed efforts. Efficacy results of Thailand's first dengue vaccine trial to immunize people against all four strains of the mosquito-borne virus should be known by the end of 2012.

'We've been working on a dengue vaccine for the better part of 60 years and for the first time in those 60 years we have a potential candidate that actually shows great promise,' said Duane Gubler, director of the emerging infectious disease faculty at Duke-NUS Graduate Medical School, Singapore.

Dengue is a mosquito-borne virus, actually four different viruses, that infects about 220 million people annually, with two million developing dengue hemorrhagic fever which can be deadly.

The virus is endemic to South-East Asia, but with urbanization and globalization it has spread rapidly throughout the tropical world, with the number of reported cases increasing ten-fold between the 1970s and now, Gubler said.

Thai scientists have been researching a dengue vaccine for the past 20 years, and now, with the assistance of Sanofi Pasteur, appear on the cusp of a breakthrough.

Since 2009, scientists from Thailand's Mahidol University have been dosing 4,000 children in Ratchburi province, which has the highest incidence of dengue nationwide, with a vaccine jointly developed by Mahidol and Sanofi Pasteur.

'So far the vaccine seems to be very safe, with very few clinical reactions after each vaccination,' said Arunee Sabcharoen, senior clinical researcher at Mahidol's faculty of tropical medicine.

Despite the uncertainty of the outcome of the trial, Sanofi Pasteur has already started construction of a 300 million euros dengue vaccine facility in Neuville-sur-Saone, France.

'We decided in 2009 to start the construction of a building to supply the world with 100 million doses,' said Jean Lang, dengue vaccine program head of Sanofi Pasteur. 'We hope the vaccine will be available by 2014,' he said.

Scientists have encountered numerous obstacles in finding a dengue vaccine, including the fact that it could not be tested on animals (the virus only infects humans), and because there are four strains, each of which requires building up a different immunity.

Furthermore, since the virus tends to prevail in poor, third-world countries, giant pharmaceutical firms were generally disinterested in investing in the research and development of a vaccine.

Gubler attributed the seeming success of the Thai vaccine trial to access to research funding and a technological breakthrough.

'The breakthrough that allowed the current vaccine to proceed was the ability to construct infectious clones of the virus, and to genetically engineer a vaccine that protects against all four viruses,' he said.