Antivirals are now available for a wide variety of viral diseases.
Ribavirin has few side effects, but is prohibitively expensive for all but the most serious cases. Amantadine, which is effective against strains of influenza A, acts by interfering with viral uncoating. Although not a cure, the drug lessens the frequency and severity of outbreaks. Study at this level was not possible until electron microscopes became available and it is only in last 20 years that antiviral drugs have been on the market. See also nucleic acid , virus , retrovirus .