The work is a collection of 5 researches, with original results and with knowledge contributions in the clinical-epidemic field, such as:

• a) The secondary infection for a second Dengue fever serotype behave as a main risk factor of Hemorrhagic Fever (HF), even 20 years after the primeinfection,
• b) It was demonstrated the existence of Den 2 stupms producers of HF, able to produce the silent transmission in the course of a primeinfection,
• c) Hospitalization stages and deceased by DHF were estimated for the first time according to ages, in individuals with Den 2 secondary infection.
• d) It is demontrated that age is an important factor in Den 2 secondary infections.
• e) It was documented the increase in the epidemic’s severity in 1997, as it developed,
• f) It was supported the role of antibodies of cross-reactivity as a risk factor. This work contributes to explain the causes of morbi-mortality by Dengue and the understanding of this disease’s pathogenesis. This group of researches has generated 8 publications in very prestigious international magazines in this field and it has been presented in 8 important international events.