Press Release

VX-950, Investigational Oral Hepatitis C Protease Inhibitor, Demonstrates Rapid and Dramatic Reduction in Viral Levels in Combination with Pegylated Interferon

Cambridge, MA, January 9, 2006- New data announced today by Vertex Pharmaceuticals Incorporated (Nasdaq: VRTX) show that VX-950, an investigational oral hepatitis C virus (HCV) protease inhibitor, dosed in combination with pegylated interferon alfa-2a (Pegasys'; peg-IFN), achieved a rapid and dramatic reduction in plasma viral RNA levels in patients with chronic genotype 1 HCV infection. In this Phase Ib study, the combination of VX-950 and peg-IFN produced an initial median reduction in plasma HCV RNA of more than 3 log10 in the first two days, followed by continued decline to a median 5.5 log10 reduction in HCV RNA at day 14, which equates to a 300,000-fold reduction in viral levels. The majority of patients (6 of 8) receiving the combination achieved HCV RNA levels below the limit of quantitation (30 IU/mL, as measured by the Roche TaqMan® assay) at 14 days, with 4 of 8 patients achieving HCV RNA levels below the limit of detection (10 IU/mL, Roche TaqMan®). The antiviral activity of the combination through 14 days was significantly greater than the activity of VX-950 administered as a single agent, and much greater than peg-IFN alone. In addition, VX-950 appeared to be well-tolerated when dosed alone and in combination with peg-IFN in the study. The full data set will be presented at a medical conference later this year.

"These data show that VX-950, in combination with pegylated interferon, produced a very rapid viral response in each of these genotype 1 patients, who are historically the most difficult to treat effectively," said Henk W. Reesink, MD, Associate Professor of Medicine at Academic Medical Center in Amsterdam, and a lead investigator for the study. "The profound decreases in viral load strongly support the evaluation of VX-950 in combination with pegylated interferon as part of a three-month treatment paradigm to achieve sustained viral responses (SVR) in HCV patients."

Study Design and Results

The 14-day, randomized, blinded, placebo-controlled Phase Ib study enrolled 20 treatment-naïve patients with genotype 1 HCV, the most prevalent and difficult to treat form of HCV infection. Patients were randomized to receive a new tablet formulation of VX-950 at a dose of 750 mg every eight hours (q8h) in combination with a standard dose of peg-IFN (n=8), the same dose of VX-950 administered alone (n=8), or a standard dose of peg-IFN alone (n=4). The median viral load for all patients at study entry was 6.65 log10 IU/mL HCV RNA (approximately 4.4 million IU/mL). Available interim results indicate:

• A median 5.5 log10 reduction in HCV RNA in patients receiving VX-950 and peg-IFN for 14 days; 6 of 8 patients had viral levels below the limit of quantitation (30 IU/mL) at 14 days, and 4 of 8 also achieved viral levels below the limit of detection (10 IU/mL).
• A median 4.0 log10 reduction in HCV RNA in patients receiving VX-950 alone for 14 days; 1 of 8 patients had viral levels below the limit of detection (10 IU/mL).
• A median 1.0 log10 reduction in HCV RNA in patients receiving peg-IFN alone for 14 days; no patients had viral levels below the limit of quantitation (30 IU/mL) at 14 days.

Safety

A preliminary safety review has been conducted that indicates that the treatment was well tolerated. All patients completed dosing and no serious adverse events were reported. All adverse events in the patients receiving VX-950 alone were reported as mild. Typical interferon-related side effects, of mild to moderate severity, were reported in the patients that received peg-IFN along with VX-950 or placebo. Laboratory-related adverse events of neutropenia in one patient and thrombocytopenia in one patient were reported among the patients who received peg-IFN. Neutropenia and thrombocytopenia have previously been reported in patients receiving peg-IFN alone. It is not known if the two patients in whom these events occurred were also receiving VX-950, because the full safety database has not yet been unblinded. A complete safety analysis will be conducted once the study is fully unblinded.

"The data announced today provide further support for VX-950's potential to transform the standard of care in HCV," said Joshua Boger, Ph.D., Chairman, President and Chief Executive Officer of Vertex. "We look forward to pursuing additional clinical studies in 2006 that will evaluate the ability of VX-950, in combination with pegylated interferon, to achieve sustained viral responses in HCV patients, with a shorter duration of treatment compared to the current standard of care."

Clinical Plans

Vertex is conducting a broad Phase II development program designed to establish the safety and antiviral activity of VX-950 in studies of up to three months duration. In the next few months, Vertex expects to initiate a three-month Phase II trial with more than 200 participants that will study VX-950 dosed in combination with peg-IFN, both with and without ribavirin, another standard HCV treatment. This three-month study will include a comparison to the current standard of care in HCV treatment. Additionally, a 12-patient, 28-day Phase II trial of VX-950 plus peg-IFN and ribavirin has now completed enrollment and preliminary data from this study are anticipated in the first quarter. In December 2005, VX-950 received Fast Track designation from the U.S. Food and Drug Administration.

About Hepatitis C

Hepatitis C is a liver disease caused by the hepatitis C virus, which is found in the liver and blood of people with the disease. HCV, a serious public health concern affecting 3.4 million individuals in the United States, is spread primarily through direct contact with the blood of infected people. Though many people with hepatitis C may not experience symptoms nor be aware of their infection, others may have symptoms such as jaundice and fatigue. Hepatitis C significantly increases a person's risk for developing chronic liver disease, cirrhosis, the need for liver transplantation, liver cancer, or death. Current treatments are commonly dosed for six to 12 months and may be associated with significant adverse events.

About VX-950 and Previous Clinical Data

VX-950 is an oral inhibitor of hepatitis C virus protease, an enzyme essential for viral replication. In 2005, Vertex reported results from a 14-day, Phase Ib study of VX-950 dosed as a single agent in genotype 1 HCV patients. In this prior study, VX-950 displayed potent antiviral activity. After 14 days of dosing, patients in the dose group with the best response (750 mg every 8 hours) achieved a median reduction in HCV RNA of 4.4 log10, a 25,000-fold reduction in viral levels. Adverse events observed in patients receiving VX-950 that were considered possibly related to the drug were mild, and generally similar in frequency to events in patients receiving placebo. The most common adverse events reported in both placebo and VX-950 patients were headache, frequent urination and gastrointestinal symptoms.

Vertex researchers were the first to solve the three-dimensional crystal structure of HCV protease, and have used structural insights to enable the design of small molecule HCV protease inhibitors, including VX-950.

About Vertex

Vertex Pharmaceuticals Incorporated is a global biotechnology company committed to the discovery and development of breakthrough small molecule drugs for serious diseases. The Company's strategy is to commercialize its products both independently and in collaboration with major pharmaceutical companies. Vertex's product pipeline is principally focused on viral diseases, inflammation, autoimmune diseases and cancer. Vertex co-promotes the HIV protease inhibitor, Lexiva, with GlaxoSmithKline.

Safe Harbor Statement

This press release may contain forward-looking statements, including statements that (i) VX-950 has the potential to transform the standard of care in HCV infection; (ii) Vertex will pursue additional clinical studies in 2006, including a three-month Phase II trial with more than 200 patients planned for commencement in the next few months, that will evaluate the ability of VX-950 to achieve sustained viral responses (SVR) in HCV patients; and (iii) Vertex will receive preliminary data from its ongoing 28-day Phase II clinical trial in the first quarter of 2006. While management makes its best efforts to be accurate in making forward-looking statements, such statements are subject to risks and uncertainties that could cause Vertex's actual results to vary materially. These risks and uncertainties include, among other things, the risks that (i) full analysis of the data, or further testing, will not reflect the interim results reported in this press release, or support any or all of the conclusions provided in this press release; and (ii) clinical trials for VX-950 may not proceed as planned due to technical, scientific, or patient enrollment issues, clinical trial results may not be available when expected, or expected regulatory filings may not occur or may be delayed due to adverse clinical or non-clinical trial developments or unanticipated FDA action; and other risks listed under Risk Factors in Vertex's Form 10-K filed with the Securities and Exchange Commission on March 16, 2005.

Lexiva is a registered trademark of the GlaxoSmithKline group of companies, and Pegasys is a registered trademark of Hoffman-La Roche Inc.

Vertex Contacts:
Lynne H. Brum, Vice President, Strategic Communications, (617) 444-6614
Michael Partridge, Director, Corporate Communications, (617) 444-6108
Lora Pike, Manager, Investor Relations, (617) 444-6755
Zachry Barber, Specialist, Media Relations, (617) 444-6470