Antivirals: past, present and future.

Vaccination is possible to prevent infections with some viruses: hepatitis B virus (HBV), varicella-zoster virus (VZV), influenza A and B viruses, Yellow fever virus and poliovirus; but not for others: human immunodeficiency virus (HIV), hepatitis C virus (HCV), herpes simplex virus (HSV), cytomegalovirus (CMV), and most hemorrhagic fever viruses (HFV) (except for Yellow fever virus). Antiviral therapy is obviously needed to control those infections that are not amenable to prophylaxis by vaccination, but is also highly desirable for those infections where vaccination has not been implemented or did not fulfill its premises for complete protection.