It was once thought that fibrosis was irreversible, but research has shown that treatment for hepatitis C can slow or halt fibrosis progression, and potentially even reverse existing liver damage. Studies have shown that fibrosis stabilization and regression are most likely when HCV positive individuals treated with HCV therapy achieve a sustained virological response (SVR, continued undetectable HCV viral load six months after the completion of therapy), but improvement has also been seen in some partial responders and nonresponders.