Dengue virus (DV) infections cause undisputedly the most important arthropod-borne viral disease in terms of worldwide prevalence, human suffering, and cost. Worldwide DV infection prevalence in 2010 was between 284 to 528 million cases. Approximately 84% of these cases come from Asia and the Americas, where the cost for emerging economies can be as high as 580 million dollars per year. The need for an efficient vaccine against DV is extreme.
Vaccination has been the most desired strategy for controlling the spread of DV. Neutralizing antibodies directed against mosquito-borne flavivirus envelopes can prevent the development of infectious disease. This has been beautifully illustrated by the development of successful vaccines against other related mosquito-borne flaviviruses with similar structure, specifically the attenuated strain 17D vaccine against yellow fever virus (YFV) and the attenuated strain 14-14-2 against Japanese encephalitis virus (JEV), both obtained by serial passage in cell culture.
Why then has the development of a DV vaccine proven so challenging? Natural DV infection triggers a robust, neutralizing immunity that provides an apparently life-long protection against the infecting DV serotype and a short-lived (months) cross-protection against heterologous DV serotypes. Interestingly, the humoral response to DV not only mediates protection though viral neutralization, but also seems to play a major role in the development of more severe forms of dengue disease. Dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) cases are often associated with secondary DV infections with a heterologous DV serotype.
There are two main windows of opportunity to build upon toward realizing efficient vaccination for DV. First, a clinically relevant animal model for dengue infection and vaccine development is lacking. Rhesus monkeys do not show clinical signs of infection after a wild-type DV challenge; instead the intensity and length of viremia serves as a proxy to infer protection. Second, rigorous correlates of protection have not been established for DV. The best available indicator of immunogenicity is the titration of neutralizing antibodies, however titration of plaque reduction neutralization antibodies has not been promoted to a bona fide correlate of protection because of ambiguous results pertaining to the protective titer. Testing the protection efficiency of tetravalent vaccine candidates in volunteers may answer both questions. Results from the first human DV challenge experiments have been recently published and demonstrate the viability of this approach.