Antiviral resistance means that a virus has changed in such a way that the antiviral drug is less effective in treating or preventing illnesses with that virus.Influenza viruses has become resistant to influenza drugs. . Resistance of influenza A viruses to antiviral drugs can occur spontaneously or emerge during the course of antiviral treatment or antiviral exposure. Antiviral resistance testing involves several laboratory tests, including a specific functional assay, the neuraminidase inhibition (NI) assay, and molecular techniques to look for genetic changes that are associated with antiviral resistance. There is another class of influenza antiviral drugs called the adamantanes that are not recommended for use because of high levels of antiviral resistance to these drugs among circulating influenza viruses.