Dengue is a severe viral disease affecting 50-100 million people per year in more than 100 countries. This disease is all the more deadly because no effective vaccine has been discovered against the dengue virus. It has been particularly difficult to create vaccines against this disease because what we call the infectious ‘dengue virus’ can actually be of four subtypes- dengue 1, 2, 3 or 4. The interactions and competition between these 4 subtypes is not properly understood, and it is thought that they make possible vaccine formulations ineffective. Moreover, this virus can only infect humans, making the use of animal models uninformative.
Weakened Virus as First Dengue Virus Vaccine
Researchers have designed a candidate vaccine which is a weakened form of the dengue virus. This weakened virus (also called an attenuated virus) can activate our immune system and make it produce antibodies against the virus without attacking our body. In a recent clinical trial, this vaccine was administered in 3 doses over 1 year to 4002 school children in Thailand, and its efficacy (how much the incidence of a disease is reduced when a vaccine is administered) was tested over a period of 13 months following the third vaccination.
The results of the vaccine itself were disappointing—an efficacy of only 30.2% was seen. While the incidence of dengue Type I, III and IV were highly reduced, the incidence of dengue II infection remained unchanged in cases (people who were administered the vaccine) and controls (those who weren’t on the vaccine). The researchers propose that the DENV type II virus that is circulating in Thailand is different from the strain used to create the vaccine, and the antibodies generated by the vaccine are not specific enough to the virus to attack it.
More clinical trials are underway in regions with dengue endemics. These will give a better picture of the actual efficacy of these vaccines, particularly with respect to the four different subtypes. These will also tell us if it is possible to limit the severity of the infection, if not limit it entirely. This is important because severe Dengue can result in mortality. The emergence of a possible vaccine against the Dengue virus is a breakthrough in itself, and should pave the way for effective actions against the disease.
You can read about this research here.