C5 and Dengue hemorrhagic fever: In addition, clinical studies have shown that the levels of dengue NS1 and products of complement activation, including those with a known vascular effect, such as C3a, C5a, and sC5b-9, are present in higher levels in DHF patients before plasma leakage takes place, supporting the theory that complement activation is involved in the development of severe disease [12] and to deleterious patient outcomes [11], [13], [14].