Vaccine stakes upped as dengue dubbed fastest-spreading tropical disease

Many drug developers have tried and all have failed to create a vaccine for mosquito-borne dengue. And now the stakes are higher, as the World Health Organization just deemed dengue the world's fastest-spreading tropical disease, representing a pandemic threat.

A 2010 study published in Human Vaccines estimates that 2.4 billion to 3.5 billion dengue vaccine doses would be needed in the first 5 years after introduction. About 55% of the world's population lives in areas where dengue virus transmission takes place; that's 125 countries. Given the breadth of the disease--and therefore the excellent market potential for a vaccine--drug developers are doling out the cash to roll out an antidote. Various studies report anywhere from 50 million to 100 million people contract the flu-like disease each year.

"The market for a dengue vaccine is considered to be very large," Dr. Richard Mahoney, coordinator, policy and access, Dengue Vaccine Initiative, told FierceVaccines. "In theory, immunization could be delivered to all children and young adults and perhaps even older people. Since dengue particularly affects urban areas where there is more economic development and prosperity in developing countries, dengue vaccines probably have a potentially attractive private sector market."

Clinical trials are currently under way on 5 vaccine candidates, according to the Dengue Vaccine Initiative, and several more are working their way through advanced development. Sanofi ($SNY) even dropped €350 million ($440 million) on a new French factory to manufacture a three-dose vaccine. Why spend the dough? A vaccine could equal €1 billion ($1.3 billion) in sales annually.

But Sanofi's data from a Phase IIb trial in Thailand revealed lackluster results in September. The candidate vaccine showed about 30% overall efficacy against dengue fever type 2, far below the 70% efficacy estimate for which the company had hoped. Four strains of dengue exist, and Sanofi intended to protect against all. Other companies have vaccines in the pipeline, too. NIH developed a candidate live attenuated vaccine that it has licensed to four developing country manufacturers, Mahoney said. The most advanced of these licensees is the Butantan Institute in São Paulo, Brazil, whose vaccine is entering Phase II trials. Merck ($MRK) is also working on a subunit vaccine in Phase I trials and GlaxoSmithKline ($GSK) has a purified inactivated vaccine in Phase I, he said. And Inviragen's live attenuated vaccine has entered Phase II clinical trials in Puerto Rico, Colombia, Singapore and Thailand.

From a public health standpoint, the race is on. Last year, 2,000 people were infected on the Portuguese Atlantic island of Madeira, marking the first sustained dengue outbreak in Europe since the 1920s. And Asia, Africa and Latin America continue to take major hits.

- get more from Reuters
- here's the WHO press release