Results of the first ever trial to show that a safe and effective dengue vaccine may be possible are published Online First in The Lancet.
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.
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 4002 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.
2669 children were given the CYD-TDV vaccine, and 1333 given a placebo. Overall, there was no statistically significant difference between the number of dengue cases recorded in the vaccine (76 cases or 2.8% of the vaccine group) and control groups (58 cases or 4.4% of the control group). However, secondary tests showed that the vaccine was effective against DENV 1, 3 and 4 (in the range of 60 to 90%), with only DENV 2 appearing to be resistant to the effects of the vaccine in this trial. Furthermore, CYD-TDV appears to be safe and well-tolerated, with no vaccine-related serious adverse events being reported in the group who received it.