Abstract
The chapter discusses the need for chemotherapy and prophylaxis against viral diseases. It briefly mentions clinical diseases and syndromes such as influenza, respiratory tract infections, hepatitis, and arbovirus infections resulting from virus infections. Viruses causing respiratory diseases, as well as many other diseases in humans are also discussed in the chapter. It describes the vaccines that are used to check the attack of different viruses as well as their cost-effectiveness. There is a list of some viruses that have been ranked according to different variables in an attempt to select a good candidate for an antiviral drug. The incidence of the viral disease is naturally an important factor, as is the severity of the disease. The incidence can be obtained for diseases being reported in accordance with local regulations, but in many cases viral diseases are not reported and the incidence has to be calculated from different surveys. Also, a grading of the severity is not easy and an example is when herpesvirus infections are handled as a group, which includes both herpes encephalitis and cold sores. The greatest challenges and probably the most difficult and medically important areas for prophylaxis and therapy of viral diseases are the viruses that are rapidly changing in antigenic composition and/or viruses with animal reservoirs (influenza and arboviruses) and those forming latent infections (herpesviruses).