Updated with a corrected research report from Jefferies, noting that the end-of-treatment response to daclatasvir and GS-7977 was actually 97%, not 93%. BOSTON ( TheStreet) -- An early peek at data from a closely watched mid-stage study combining hepatitis C drugs from Bristol-Myers Squibb ( BMY) and Gilead Sciences ( GILD) has leaked in advance of the European Association for the Study of the Liver (EASL) annual meeting. Ninety-seven percent of genotype 1 hepatitis C patients treated with Bristol's daclatasvir and Gilead's GS-7977 has undetectable viral levels after 12 weeks of treatment. For genotype 2/3 patients, the 12-week response rate was 90%, according to a research note published Monday by Jefferies analyst Thomas Wei. Wei called the end-of-treatment response to daclatasvir-GS-7977 "encouraging" and "positive." These data from Bristol and Gilead were supposedly embargoed by EASL and were therefore not made available to the public when research abstracts for the EASL meeting were posted online on April 4. In an email to clients Monday, Jefferies said the Bristol-Gilead abstract was "briefly posted" on EASL's web site over the weekend before being taken down. Officials with EASL have not responded to questions regarding the leak of the research abstract. Interim results from a phase II study combining Bristol's NS5a inhibitor daclatasvir (BMS-52) with Gilead's GS-7977 in genotypes 1, 2, and 3 is the most highly anticipated data presentation at the EASL meeting this year. The study is important because it will be one of the first glimpses at the Hep C-killing potency of these two classes of direct-acting antivirals combined into a single, all-oral therapy. Early cure rates from the dacalatasvir-GS-7977 study -- defined as the percent of patients with undetectable viral loads four weeks after cessation of treatment -- will be presented at the EASL meeting, which takes place April 18-22. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: firstname.lastname@example.org. Follow TheStreet on Twitter and become a fan on Facebook.