Shares of Achillion Pharmaceuticals shot up as much as 20% Monday morning as it emerged that patients with hepatitis C taking its investigational therapy were cleared of the virus after just six weeks.

Interim Phase II data showed that a combination of its drug ACH-3102 and Gilead Sciences’ Sovaldi (sofusbuvir) achieved a 100% sustained virological response in treatment-naïve patients with genotype 1 forms of the disease.

If successful, the regimen could potentially offer a much shorter treatment option (eight weeks with Gilead’s Harvoni is the shortest available so far) that is free of interferon and ribavirin, which are both linked with nasty side effects.

“We believe that these results with ACH-3102 represent the shortest duration and highest response achieved to date with any two-drug, direct-acting antiviral regimen for HCV,” said Milind Deshpande, Achillon’s chief executive, noting that the firm will now evaluate “four- and six-week treatment durations that leverage all of our HCV assets including ACH-3102, ACH-3422, and sovaprevir”.