SANOFI PASTEUR ANNOUNCES PRELIMINARY TRIAL RESULTS FOR A FIRST H5N1 PRE-PANDEMIC INFLUENZA VACCINE CANDIDATE WITH AN ADJUVANT

Vice President Communications sanofi pasteur: Alain BERNAL – U. S. Media Relations: Len LAVENDA Tel.: +1 570 839 7187 - Fax: +1 570 839 0955 - Sanofi Pasteur Inc. - Discovery Drive - Swiftwater, PA 18370-0187 - USA - www.sanofipasteur.com ~ Data Show that the Vaccine Is Safe, Demonstrates Immunogenicity and Provides Future Direction For Development ~ Lyon, France – December 15, 2005 – Sanofi pasteur, the vaccines business of the sanofi-aventis Group, announced today that preliminary results of clinical trials fielded in France of an adjuvanted candidate H5N1 pre-pandemic influenza vaccine demonstrated a good immune response in a significant number of volunteers. This is the first trial of an H5N1 pre-pandemic influenza vaccine candidate that compared vaccines with and without adjuvants. Preliminary results showed that the vaccine is safe and well-tolerated in 300 healthy volunteers. A 30 microgram-dose with an adjuvant in a two-dose regimen demonstrated an immune response at levels consistent with requirements of regulatory agencies for licensure of seasonal influenza vaccine. Sanofi pasteur characterized the preliminary results as a sign of progress and providing direction for further development of a pandemic influenza vaccine. The company also noted that immune responses were detected in a number of volunteers receiving lower doses. Subsequent trials will explore different dosages, which may be helpful in answering questions about dose-sparing strategies and which is being widely discussed among the public health community. The trial was sponsored by sanofi pasteur and fielded in three sites in France: Necker and Cochin Hospitals in Paris, and Garches Hospital, with Professor Jean-Louis Bresson as the principal investigator. The vaccine used the reference strain provided by the UK’s National Institute for Biological Standards and Control (NIBSC). Assays were performed at NIBSC and the UK Health Protection Agency. As definitive results become available, they will be presented and published, as well as submitted to appropriate regulatory authorities for review. The data will be submitted as part of the company’s core “mock up” vaccine dossier to the European Agency for the Evaluation of Medicinal Products (EMEA). The core dossier has been developed in strict accordance to the EMEA guidelines. This process is expected to reduce the time necessary for approval of a pandemic vaccine in Europe once a strain is identified and a pandemic is declared. Follow-up studies, currently being planned, will be performed using vaccine produced at large scale, which will mimic the manufacturing scale that will be used during a declared pandemic. This is one of a number of initiatives by the company to help prepare the world for the possibility of an influenza pandemic. · Sanofi pasteur is investing in a major expansion of its influenza vaccine production capacity in the US, and also of its vaccine production capacity in France (Val de Reuil facility). · Sanofi pasteur has entered into an agreement with the French Ministry of Health to produce pre-pandemic vaccine in 2005 to create a 1.4 million dose stockpile with the H5N1 candidate studied in this trial. By this agreement, the company could also provide enough vaccine to protect up to 28 million people in the event of a pandemic being declared, once the actual virus strain responsible is identified. · Sanofi pasteur has entered into a series of contracts with the US government to increase that country’s pandemic preparedness efforts. The contracts include investigational doses for clinical trials; bulk vaccine for stockpiles; establishment and maintenance of laying flocks to enable year-round egg production (not just seasonal), as well as a contract to speed the production process for new cell culture influenza vaccines, including the design of a USbased cell-culture vaccine manufacturing facility. · A contract has also been signed with the Australian government for the supply of vaccine in the event of a pandemic influenza outbreak. There are also contacts concerning pandemic preparedness between sanofi pasteur and other governments in Europe and worldwide · In addition, sanofi pasteur is the only vaccine manufacturer to participate in FLUPAN, an EU-funded collaboration. FLUPAN partners include the National Institute for Biological Standards & Control (NIBSC - UK), the University of Reading (UK), Istituto Superiore di Sanita, (Italy), the Health Protection Agency (UK), and the University of Bergen (Norway). FLUPAN is intended to improve the level of pandemic preparedness in the EU. Sanofi pasteur is to produce a vaccine to combat another strain with pandemic potential (H7N1) that will be used in a FLUPAN clinical study. Influenza Overview Influenza is a highly contagious virus that is spread easily from person to person, primarily when an infected individual coughs or sneezes. An influenza pandemic is a global epidemic of an especially virulent virus with the potential for severe morbidity and mortality. According to the World Health Organization (WHO), the next pandemic is likely to result in 1 to 2.3 million hospitalizations and 280,000 to 650,000 deaths in industrialized nations alone. Its impact will most likely be even more devastating in developing countries. About sanofi-aventis Sanofi-aventis is the world’s third-largest pharmaceutical company, ranking number one in Europe. Backed by a world-class R&D organization, sanofi-aventis is developing leading positions in seven major therapeutic areas: cardiovascular disease, thrombosis, oncology, metabolic diseases, central nervous system, internal medicine, and vaccines. Sanofi-aventis is listed in Paris (EURONEXT: SAN) and in New York (NYSE: SNY). Sanofi pasteur, the vaccines business of the sanofi-aventis Group, sold nearly a billion doses of vaccine in 2004, making it possible to protect more than 500 million people across the globe, which is about 1.4 million per day. The company offers the broadest range of vaccines, providing protection against 20 bacterial and viral diseases. For more information, please visit: www.sanofipasteur.com Forward-Looking Statements This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995. Forward-looking statements are statements that are not historical facts. These statements include financial projections and estimates and their underlying assumptions, statements regarding plans, objectives and expectations with respect to future operations, products and services, and statements regarding future performance. Forward-looking statements are generally identified by the words “expect,” “anticipates,” “believes,” “intends,” “estimates,” “plans” and similar expressions. Although sanofiaventis’ management believes that the expectations reflected in such forward-looking statements are reasonable, investors are cautioned that forward-looking information and statements are subject to various risks and uncertainties, many of which are difficult to predict and generally beyond the control of sanofiaventis, that could cause actual results and developments to differ materially from those expressed in, or implied or projected by, the forward-looking information and statements. These risks and uncertainties include those discussed or identified in the public filings with the SEC and the AMF made by sanofi-aventis, including those listed under “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements” in sanofi -aventis’ annual report on Form 20-F for the year ended December 31, 2004. Other than as required by applicable law, sanofi -aventis does not undertake any obligation to update or revise any forward-looking information or statements. Sanofi-aventis subsidiaries in the United States include Sanofi -Synthelabo Inc., Aventis Pharmaceuticals Inc. and Sanofi Pasteur Inc.