Dengue is one of the most widespread mosquito-borne viral diseases in the world, with WHO estimating that around half of the world’s population are currently at risk. While infection usually causes flu-like symptoms, it can develop into a more serious form of the disease, known as severe dengue, which is a leading cause of severe illness and death among children in some Asian and Latin American countries. The incidence of dengue appears to have grown dramatically in recent decades – before 1970 only nine countries had experienced severe dengue epidemics, but the disease is now thought to be endemic in more than 100 countries across the world, according to a paper published in The Lancet. The disease is also increasingly becoming an epidemic in Pakistan. Over 50,000 people have been infected by the disease and several hundreds have died. Dengue has been specifically severe in Punjab, especially in Lahore, where the government has taken extraordinary steps to prevent the disease from spreading.
There is currently no vaccine to protect against dengue, and efforts to develop one have been hampered by the fact that dengue is not caused by a single virus, but rather four different related viruses (known as DENV 1, 2, 3 and 4), making development of an effective vaccine considerably more complicated than for some viral diseases. Furthermore, the disease appears to be unique to humans, meaning that scientists cannot use animal models to test prospective vaccine candidates.
Several possible dengue vaccine candidates are currently in development, but the new results are the first to be published showing that an effective and safe dengue vaccine may be possible. Researchers based in France and Thailand tested the effectiveness of a vaccine candidate called CYD-TDV on a group of 4,002 schoolchildren in Thailand, aged from four to eleven years old. The trial took place in Thailand because dengue is known to be endemic in this area, and local residents have a good awareness of the disease and its symptoms.
However, the vaccine proved only 30 percent effective-far less than hoped. The result leaves uncertain the future of a product that Sanofi has previously said could generate more than 1 billion euros ($1.3 billion) in yearly sales. But researchers said it did show for the first time that a safe vaccine was possible. The disappointing outcome was down to the vaccine’s failure to protect against one type of dengue virus, which turned out to be the prevalent one in Thailand at the time of the study. Hopes had been high for the closely watched Thai trial, given the fact that dengue belongs to the same virus class as yellow fever and Japanese encephalitis, both of which are controlled with highly effective existing vaccines. But it seems that making a mixed dengue vaccine containing four different virus strains can produce uneven results, underscoring the complexity of a disease that scientists have been trying to develop a vaccine against for over 70 years.
“Even if not perfect, ChimeriVax will be used, but it will not be the vaccine that will eradicate dengue,” said Eric Le Berrigaud, an analyst at stockbroker Bryan Garnier.
Despite the disappointment, Jean Lang, Sanofi’s head of dengue vaccine development, said the Phase IIb study involving 4,002 Thai children was encouraging, given the protection provided against three of the virus strains. Efficacy was around 60 percent against dengue virus type 1 and 80-90 percent against types 3 and 4. Interestingly, a single dose of the vaccine proved roughly as good as three doses.
Sanofi is conducting final-stage Phase III trials with 31,000 participants in Asia and Latin America.
Efficacy was around 60 percent against dengue virus type 1 and 80-90 percent against
types 3 and 4.”
Vaccine for dengue fever shows a glimmer of hope
