This drug is approved around the world for the treatment of chronic hepatitis C (including patients with HIV co-infection, cirrhosis, 'normal' levels of ALT) and has recently been approved (in the EU, U.S., China and many other countries) for the treatment of chronic hepatitis B.
Peginterferon alfa-2a is a long acting interferon. Interferons are proteins released in the body in response to viral infections. Interferons are important for fighting viruses in the body, for regulating reproduction of cells, and for regulating the immune system.
For genotype 1 hepatitis C treated with pegylated interferon-alpha-2a or pegylated interferon-alpha-2b (brand names Pegasys or PEG-Intron) combined with ribavirin, it has been shown that genetic polymorphisms near the human IL28B gene, encoding interferon lambda 3, are associated with significant differences in response to the treatment. This finding, originally reported in Nature, showed genotype 1 hepatitis C patients carrying certain genetic variant alleles near the IL28B gene are more likely to achieve sustained virological response after the treatment than others. Another report in Nature  demonstrated the same genetic variants are also associated with the natural clearance of the genotype 1 hepatitis C virus.
A Cochrane Review sought to determine whether interferon alfa-2a (Roferon-A) could be used as a treatment for individuals with neovascular age-related macular degeneration. The trial examined showed no evidence of Roferon-A improving visual acuity among patients with AMD, with potential harm rather than benefit.