Dengue vaccine roll-out: getting ahead of the game

For Luiz Jacintho da Silva, director of the Dengue Vaccine Initiative, the spread of dengue is a matter of the gravest concern. "Over the past few decades the disease has spread dramatically," says da Silva, noting in particular the toll it has taken on the urban poor living in the shanty towns of Asia and Latin America. Dengue, a mosquito-borne viral infection, causes severe flu-like symptoms, but can develop into potentially deadly haemorrhagic fever. It is carried mainly by the Aedes aegyptii mosquito, which breeds in water-filled containers such as discarded tyres, tin cans or oil drums. The estimated incidence of the disease has increased 30-fold over the past 50 years with 50 million dengue infections now occurring worldwide each year. Because dengue is caused by four serologically related but distinct viruses, an effective dengue vaccine needs to induce a protective immune response against all four viruses simultaneously. In drug industry parlance it must be tetravalent. Until now this hurdle has been insurmountable, but French vaccine company Sanofi-Pasteur announced this year that it has a viable tetravalent dengue vaccine undergoing phase III trials in Australia. [ILLUSTRATION OMITTED] This means that in smaller trials the vaccine has been shown capable of producing an immune response and that it is now a matter of confirming those results by demonstrating protection against the disease and monitoring side-effects in a larger group. "The goal is to make the dengue vaccine available as early as 2015," says Michael Watson, vice president of global immunization policy at Sanofi-Pasteur. "In the past, when new vaccines were developed, it took years for them to reach people in developing countries on a large scale. The vaccine for hepatitis B took more than 10 years and one for HiB (Haemophilus influenzae type b) also took a long time, despite a high disease burden," says Joachim Hombach, acting head of WHO's Initiative for Vaccine Research. "A future dengue vaccine would try to repeat what has been done with vaccines for rotavirus and pneumococcal disease, when the time it took between licensing and introduction of the vaccine in developing countries was massively reduced," Hombach says. The Dengue Vaccine Initiative, a Bill and Melinda Gates-funded project launched in February of this year, headed by da Silva, works towards this goal. "We are working with public health programmes, vaccine producers and international organizations, such as WHO, to make sure the dengue vaccine will have an early introduction," da Silva says. Sanofi-Pasteur is keen to move forward with the preparations for roll-out and--instead of going the usual route of so-called travel vaccines where wealthy westerners get the vaccine first and the endemic populations are the last to benefit--it wants the vaccine to go straight to the endemic countries. As laudable as this intention may be, it raises several issues regarding distribution, notably with regard to supply and demand. "There will not be sufficient vaccine for all in the beginning," says da Silva. This means that there are going to be some difficult decisions about who gets it first. Unfortunately, to make those decisions, Sanofi-Pasteur and its partners need epidemiological information that is currently unavailable. "Available epidemiological data, with few exceptions, are inadequate," says da Silva. "They are barely sufficient to make educated guesses on vaccination policies." One of the reasons for this is the way dengue tends to blend into the background. "The disease can be easily misdiagnosed due to the fact that its clinical features are common to a host of other infectious diseases," da Silva says. Another reason for the paucity of data is the lack of disease surveillance in endemic countries. According to Ciro de Quadros, executive vice president of the Sabin Vaccine Institute, Africa is a matter of particular concern in this regard. …