Immunology
Infection with one dengue serotype confers long- lasting type-specific protection, a benefit that may be more apparent than real because the type-specific protection also brings a greatly increased susceptibility to severe dengue disease in the event of infection with dengue virus of another serotype.
Epidemiological studies clearly link the severe forms of dengue disease to previous dengue infection and to transplacental acquisition of maternal dengue antibody.Dengue virus infects mononuclear phagocytes, and there is both in vitro and in vivo evidence that the interaction is facilitated and severe infection more likely when antibody to another dengue serotype is present. This phenomenon alone has important implications for the development of dengue vaccines. Administration of monovalent or polyvalent vaccines, even if they were now available for human use, carries with it serious risk of predisposing partially immune populations to further and more serious dengue virus disease.
Secondary dengue infections that carry no risk of dengue hemorrhagic fever or dengue shock syndrome can occur when sequential dengue infections occur at intervals of 5 or more years, when sequential infections do not end with dengue type 2, and when two or more dengue viruses, including type 2, are endemic in the same area. Malnourished children and alpha-thalassemia patients have a greatly reduced risk of dengue hemorrhagic fever and dengue shock syndrome.