Business Wire - September 19, 2003

The HIV Vaccine Trials Network (HVTN) and Merck & Co., Inc. today announced that they have begun the first global clinical trial of Merck's HIV vaccine candidate in 18 cities around the world. The trial is the first study of an HIV vaccine candidate to take place in so many global locations simultaneously. The trial is also the first collaboration between Merck and the HVTN, a global clinical research network supported by the National Institute of Allergy and Infectious Diseases (NIAID), one of the National Institutes of Health (NIH).

"This trial is significant both for its global scope and because it initiates the kind of public/private partnership that is crucial to fighting the pandemic of HIV/AIDS," said Jeffrey Chodakewitz, M.D., vice president, Clinical Research, at Merck. "We've combined Merck's ability to develop and manufacture vaccines with the HVTN's worldwide network of trial sites for testing vaccine candidates."

With approximately 14,000 new HIV infections each day, 95 percent of which occur in developing countries, testing vaccine candidates in all affected regions, and in locations in which there are different viral strains is of crucial importance.

"We are pleased to work with Merck in testing their investigational HIV vaccine candidate on a truly global scale," said Lawrence Corey, M.D., principal investigator of the HVTN. "Clinical trials involving a broad range of populations are key to building the body of knowledge we need to develop a vaccine that is generally well tolerated and effective in all populations worldwide."

The study will be conducted in diverse populations in North America, South America, the Caribbean, Southern Africa and Southeast Asia using the HVTN's network of clinical trial sites in combination with a number of Merck sites. The HVTN and Merck sites taking part in the trial are located in the United States, Puerto Rico, Brazil, Haiti, Malawi, Peru, South Africa and Thailand. No live HIV is used in the production of the vaccine candidate, so the vaccine candidate cannot cause HIV infection or AIDS.

About 435 adult volunteers who are not infected with HIV will participate in the study, which is designed to establish if the vaccine candidate is safe, well-tolerated, practical to administer in different regions of the world and capable of stimulating an effective immune response to HIV in humans. Based on these immune responses, the study will also examine whether differences in genetic background, nutritional status and HIV strains may prove important to the safety and effectiveness of HIV vaccines.

Scientists caution that it will be years before a vaccine for HIV could become available for widespread use. Any vaccine must be carefully tested, refined, and approved to establish the safety and effectiveness of the final product. Merck began testing its HIV vaccine candidates in humans in the United States in late 1999, and is currently running simultaneous trials of its vaccine candidates.

The collaborative trial will test Merck's HIV vaccine candidate -- known as an HIV-1 gag replication-defective adenovirus -- which is based on a common cold virus that has been modified so that it cannot reproduce and cause illness. The adenovirus is used as a vector, or a delivery vehicle, to transport a synthetically produced gene, or tiny fragment of HIV-1 known as gag, into the cells. The delivery of the HIV-1 gene into the cells stimulates the body to generate a potent cellular immune response to HIV-1, producing an army of killer cells (called T-cells) that are programmed to recognize and kill HIV-1 infected cells.

Public/Private Partnership

The international study is the first collaboration between the HVTN, which was established in 2000 by the NIAID, a division of the NIH, and Merck, whose scientists have been conducting research to develop an HIV/AIDS vaccine for more than 15 years. It is hoped that the collaboration may help increase the likelihood of developing a generally well tolerated and effective vaccine against HIV/AIDS. This effort is an example of the type of public/private partnership that brings collective strengths to bear on one of the world's most serious health problems.

Merck has a long history of addressing major public health needs through the development of vaccines for measles, mumps, rubella, hepatitis A and B, pneumococcal infection and varicella. In addition to Merck's ongoing HIV vaccine research and development program, the company is conducting research to develop new medicines for the treatment of HIV/AIDS.

About Merck

Merck & Co., Inc. is a global research-driven pharmaceutical products and services company. Merck discovers, develops, manufactures and markets a broad range of innovative products to improve human and animal health, directly and through its joint ventures.

About The HIV Vaccine Trials Network

The HVTN is an international collaboration of scientists and institutions whose goal is to accelerate the search for an HIV vaccine by sharing trial results and facilitating parallel, concurrent testing. The HVTN is a unique hybrid that combines the depth and diversity of the academic community and the flexibility of a commercial drug company. Working with industry and government, the HVTN seeks to expedite and coordinate the trial process, advancing vaccine candidates and building a body of knowledge around HIV vaccine trials.

The HVTN is funded and supported by the NIAID of the NIH, an agency of the U.S. Department of Health and Human Services (DHHS). The HVTN is comprised of 25 research institutions worldwide, coordinated from its headquarters at the Fred Hutchinson Cancer Research Center in Seattle.

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 involve risks and uncertainties which may cause results to differ materially from those set forth in the statements. The forward-looking statements include statements regarding product development and product potential. No forward-looking statement can be guaranteed, and actual results may differ materially from those projected. Additional detailed information concerning a number of factors that could cause actual results to differ materially is available in Item 1 of Merck's Annual Report on Form 10-K for the year ended Dec. 31, 2002, in its periodic reports on Form 10-Q and in its reports on Form 8-K (if any). Copies of these forms are available on request to Merck's Office of Stockholder Services.

CONTACT: Merck & Co., Inc.

Press:

Janet Skidmore, 908-423-3046

732-221-0390 - mobile

Investor Contact:

Mark Stejbach, 908-423-5185

or

HVTN

Press:

Steve Wakefield, 206-667-6705

Lisabeth Bull, 206-667-1820

SOURCE: Merck & Co., Inc.

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