The U.S. Food and Drug Administration (FDA) is extending the review period for the Biologics License Application (BLA) for ZOSTAVAX® [zoster vaccine live (Oka/Merck)], Merck's investigational shingles vaccine, to review additional information that Merck submitted during the review process. The FDA has informed Merck that the agency's new review goal date for the application for ZOSTAVAX is May 25.

Merck filed the BLA for ZOSTAVAX with the FDA on April 25, 2005. The Company has filed additional regulatory applications for ZOSTAVAX in other major markets including the European Union and Australia.

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 merck.

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 cautionary statements in Item 1 of Merck's Form 10-K for the year ended Dec. 31, 2004, and in its periodic reports on Form 10-Q and Form 8-K, which the company incorporates by reference.

ZOSTAVAX is the Merck registered trademark for zoster vaccine live (Oka/Merck).

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