there is no vaccine to protect against dengue..

There is no vaccine to protect against dengue. Although progress is underway, developing a vaccine against the disease is challenging. With four different serotypes of the dengue virusthat can cause the disease, the vaccine must immunize against all four types to be effective. Vaccination against only one serotype could possible lead to severe DHS when infected with another serotype due to Antibody-Dependent Enhancement. There is still limited knowledge of how the disease typically behaves and how the virus interacts with the immune system. Another difficulty is that there is no reliable animal model for DHF and thus also not a suitable animal model to test immune responses to potential vaccines. In addition, progress in vaccine development is slow mainly because dengue viruses grow poorly in cell culture (see alsoClinical Trials).