Interferon alfa biologics were the ninth largest selling class of biological products, with total sales in 2005 estimated at $2.11 billion.

Natural interferon is a protein produced by the body's cells in response to viral infections. There are three types: alfa, beta and gamma.

Genetically engineered interferon alfa mimics the activity of naturally-occuring interferon alfa produced by the body. The drug has some direct antiviral effects, and also stimulates the body's immune system to fight foreign organisms.

The leading interferon alfa biologics are: