Pegylated interferon alfa-2a, also known as Pegasys, is a medication used to treat certain viral infections, including hepatitis B and C. It is a form of interferon that has been modified with polyethylene glycol (PEG) to increase its effectiveness and prolong its action in the body. By binding to specific receptors on cells, pegylated interferon alfa-2a helps to boost the immune response and fight off the viral infection. It is administered via injection and is typically used in combination with other medications for optimal treatment outcomes.