Uses: Peginterferon alfa-2a is used alone or in combination with ribavirin to treat chronic hepatitis C, a viral infection of the liver. It is also used to treat chronic hepatitis B infection. This medication reduces the amount of hepatitis C virus in the body and helps the body's immune system fight the infection. It is not known if peginterferon can cure hepatitis C virus infections (permanently eliminate the virus from your body). It is also not known if this drug can prevent you from passing the virus to others. Practice "safe sex" (including the use of latex condoms) to lower the risk of passing the virus to others.