Since spontaneous mutagenesis and quasi-species rearrangements of the RNA-containing viruses, as well as an absence of both viral and cellular RNA reparation systems, causes resistance to originally effective antiviral drugs, combination therapy with nucleoside and non-nucleoside inhibitors of the viral enzymes in combination with immunomodulators is recommended. The use of specific immunoglobulins does not result in complete elimination of the flaviviruses but rather in possible antibody-dependent enhancement of the flavivirus infection by means of increased penetration of complexes of virions with specific antibodies into cells with receptors for Fc-fragments of immunoglobulins.