Dynavax Technologies Corporation and Merck Update Status of Clinical Hold of Investigational Vaccine HEPLISAV

Dynavax Technologies Corporation and Merck Update Status of Clinical Hold of Investigational Vaccine HEPLISAV

4/17/2008

BERKELEY, Calif. & WHITEHOUSE STATION, N.J. -- Dynavax Technologies Corporation (Nasdaq:DVAX) and Merck & Co, Inc. announced today the receipt of formal written notification from the US Food and Drug Administration (FDA) detailing a request for information relating to the previously announced clinical hold placed on the two Investigational New Drug Applications for HEPLISAVTM, an investigational hepatitis B vaccine being jointly developed by Dynavax and Merck for use in adults and in patients with end stage renal disease. The FDA is requesting a review of clinical and preclinical safety data for HEPLISAV. Additionally, the FDA has requested all available information about the single case of Wegener's granulomatosis reported in the Phase 3 trial. Dynavax and Merck plan to provide a complete response to the FDA query in a timely manner. The FDA will then determine whether the data provided are satisfactory for the continuation of the clinical program.

Dynavax Technologies Corporation discovers, develops, and intends to commercialize innovative TLR9 agonist-based products to treat and prevent infectious diseases, allergies, cancer, and chronic inflammatory diseases using versatile, proprietary approaches that alter immune system responses in highly specific ways. Our TLR9 agonists are based on immunostimulatory sequences, or ISS, which are short DNA sequences that enhance the ability of the immune system to fight disease and control chronic inflammation. Our product candidates include: HEPLISAV, a hepatitis B vaccine in Phase 3 partnered with Merck & Co. Inc.; TOLAMBATM, a ragweed allergy immunotherapy in Phase 2; a therapy for non-Hodgkin's lymphoma (NHL) in Phase 2 and for metastatic colorectal cancer in Phase 1; and a therapy for hepatitis B also in Phase 1. Our preclinical asthma and COPD program is partnered with AstraZeneca. The National Institutes of Health (NIH) partially funds our preclinical work on a vaccine for influenza. Symphony Dynamo, Inc. (SDI) funds our colorectal cancer trials and our preclinical hepatitis C therapeutic program, and Deerfield Management has committed funding for our allergy programs. While Deerfield, NIH and SDI provide program support, Dynavax has retained rights to seek strategic partners for future development and commercialization. For more information, please visit http://www.dynavax.com.

About Merck

Merck & Co., Inc. is a global research-driven pharmaceutical company dedicated to putting patients first. Established in 1891, Merck currently discovers, develops, manufactures and markets vaccines and medicines to address unmet medical needs. The Company devotes extensive efforts to increase access to medicines through far-reaching programs that not only donate Merck medicines but help deliver them to the people who need them. Merck also publishes unbiased health information as a not-for-profit service. For more information, visit www.merck.com.

Dynavax Forward-looking Statement

This press release contains "forward-looking statements," including statements related to the clinical status of HEPLISAV, the nature and timing of communications with the FDA regarding the current clinical hold and whether or not and under what additional requirements, if any, further clinical development will be permitted. Actual results may differ materially from those set forth in this press release due to the risks and uncertainties inherent in our business, including difficulties or delays in development, initiation and completion of clinical trials, the results of clinical trials and the impact of those results on the initiation and completion of subsequent trials and issues arising in the regulatory process; achieving our Merck collaborative agreement objectives and obtaining regulatory approval for HEPLISAV; the scope and validity of patent protection and the possibility of claims against us based on the patent rights of others; our ability to obtain additional financing to support our operations; and other risks detailed in the "Risk Factors" section of our Annual Report on Form 10-K. We undertake no obligation to revise or update information herein to reflect events or circumstances in the future, even if new information becomes available.

Merck Forward-Looking Statement

This press release contains "forward-looking statements" as that term is defined in the Private Securities Litigation Reform Act of 1995. These statements are based on management's current expectations and involve risks and uncertainties, which may cause results to differ materially from those set forth in the statements. The forward-looking statements may include statements regarding product development, product potential or financial performance. No forward-looking statement can be guaranteed and actual results may differ materially from those projected. Merck undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events, or otherwise. Forward-looking statements in this press release should be evaluated together with the many uncertainties that affect Merck's business, particularly those mentioned in the risk factors and cautionary statements in Item 1A of Merck's Form 10-K for the year ended Dec. 31, 2007, and in its periodic reports on Form 10-Q and current reports on Form 8-K, if any, which the Company incorporates by reference.

Contact:

Dynavax Investor Relations and Media Shari Annes, 1-510-665-7210 (office) cell: 1-650-888-0902 [email protected] or for Merck Investor Relations Graeme Bell, 1-908-423-5185 or Global Communications Kelley P. Dougherty, 1-215-652-0059