Merck reported Phase-II interim results on its HCV combination therapy Monday, and the findings are a mixed bag. The triplet of grazoprevir, elbasvir and Gilead’s Sovaldi (sofosbuvir) demonstrated competitive eight-week dosing data, but missed the mark in four- and six-week regimens, analysts said.

Over four weeks of treatment, only 12 of 31 (38.7%) enrolled patients demonstrated a sustained virologic response (SVR), while among patients taking the drugs over six weeks, SVR rates reached 80% in cirrhotic and 86.7% in non-cirrhotic subjects—and both of those rates are significantly lower than those associates with drugs already available at the pharmacy. In eight weeks, however, the combo regimen demonstrated an SVR rate of 95%.

Credit Suisse analyst Vamil Divan wrote in an investor note that Merck’s attempts at creating a viable four- or six-week regimen do not “stack up” to the competition, “given the desire of physicians and patients to maximize efficacy,” and added that “Merck’s approach,” in these time frames “is simply not sufficient,” at their current SVR rates.

Seamus Fernandez, an analyst at Leerink Partners, wrote that this data, when juxtaposed with efficacy data for Gilead’s Sovaldi and all-oral Harvoni, decreases Merck’s chances of becoming a major player on the HCV treatment scene. “Based on rapidly growing experience with Sovaldi/Harvoni…it is our opinion that Merck’s only chance to be a major #2 player must assume that the Idenix nuc delivers a safety and efficacy profile comparable to Sovaldi,” Fernandez noted, “we believe this is possible, but still far from assured.”

Merck purchased Idenix Pharmaceuticals for $3.9 billion this past June, acquiring nucleotide inhibitor IDX21437 in the process.

ISI Evercore analyst Mark Schoenebaum wrote in an investor note this morning that Merck plans to start additional Phase-II studies in the first quarter of 2015 that will evaluate the recently acquired nucleotide inhibitor paired with the drugmaker’s  NS5a and antiviral MK-5172. Seven-day dosing data for this investigational combo is expected later this week at the American Association for the Study of Liver Diseases (AASLD).