Diseases caused by virus es.
Long-term immunity usually follows viral childhood diseases (see chickenpox). The common influenza ) or to keep the immune system from fighting them off (see AIDS ). Certain cancer s are caused by viruses. Vaccine s can prevent some viral diseases. Most recently developed antiviral drugs work only against specific viruses; antibiotics are ineffective against viral diseases. See also {{link=poliomyelitis">poliomyelitis ; smallpox .