Sanofi Pasteur's Dengue Vaccine in Final Stage of Clinical Development

First Phase 3 Study Underway in Australia

LYON, France, November 4, 2010 - Sanofi Pasteur, the vaccines division of sanofi-aventis Group
(EURONEXT: SAN and NYSE: SNY), announced today that its dengue vaccine is in
final stage of clinical development. Sanofi Pasteur's dengue vaccine, the
world's most clinically advanced dengue vaccine candidate(1,2), entered its
first phase 3 clinical study in Australia.

This study is part of a global phase 3 clinical study program
aimed at advancing the development of a novel vaccine for the prevention of
dengue disease in children and adults. Currently, there is no specific
treatment available for dengue fever, which is a threat to nearly three
billion people and a public health priority in many countries of Latin
America and Asia where epidemics occur.(3)

Phase 3 studies are the ultimate steps in the clinical
development of a vaccine before it is submitted to regulatory authorities for
evaluation for market authorization. Sanofi Pasteur's candidate dengue
vaccine is the first to reach phase 3 of clinical development.

"To address the global health challenge represented by dengue
fever, we are conducting an unprecedented dengue vaccine research and
development program as well as a scale up of the vaccine production," said
Wayne Pisano, President and Chief Executive Officer of Sanofi Pasteur. "We
are now entering the final laps of a long run that Sanofi Pasteur started
almost 20 years ago. If successful, we are committed to introducing the
vaccine in countries where dengue is of highest public health priority."

The study in Australia is the first to use dengue vaccine
doses produced with industrial scale processes. The study is aimed at
demonstrating that production of the vaccine at industrial scale will meet
consistency criteria required for market authorization by regulatory
authorities. Details of the phase 3 study in Australia as well as results of
already completed studies are presented at the 59th annual conference of
ASTMH (American Society of Tropical Medicine and Hygiene), held in Atlanta
(Georgia, United States), November 3-7.

Sanofi Pasteur's global dengue vaccine clinical study program

Sanofi Pasteur's candidate dengue vaccine-which targets all
four virus serotypes-has been evaluated in clinical studies (Phase 1, 2) in
adults and children in the U.S., Asia and Latin America. Overall, a balanced
immune response against all four serotypes was observed after three doses of
the vaccine. The vaccine is well tolerated with a similar safety profile
after each dose.(4)

Clinical studies in adults and children are ongoing in Mexico,
Colombia, Honduras, Puerto Rico, Peru, the Philippines, Vietnam, Singapore,
Australia, and Thailand.

About dengue fever

Dengue fever is a mosquito-borne disease caused by four dengue
virus serotypes (1 to 4). Overall, the disease is a potential threat to
almost half of the world's population. Of the estimated 220 million people
infected annually, two million-mostly children-develop dengue hemorrhagic
fever (DHF), a severe form of the disease.(5) DHF is a leading cause of
hospitalization, placing tremendous pressure on strained medical resources
and having a heavy economic and societal impact. Many factors have
contributed to the re-emergence and dramatic increase in dengue fever
including urbanization and increased travel which facilitates dissemination
of dengue viruses and the circulation of all four dengue virus serotypes.

For continuous up to date information about dengue fever
outbreaks, visit www.denguewatch.org, a news hub reporting worldwide
alerts on dengue, provided by the Pediatric Dengue Vaccine Initiative.

About sanofi-aventis

Sanofi-aventis, a leading global pharmaceutical company,
discovers, develops and distributes therapeutic solutions to improve the
lives of everyone. Sanofi-aventis is listed in Paris (EURONEXT: SAN) and in
New York (NYSE: SNY). For more information, please visit:
www.sanofi-aventis.com

Sanofi Pasteur, the vaccines division of sanofi-aventis Group,
provided more than 1.6 billion doses of vaccine in 2009, making it possible
to immunize more than 500 million people across the globe. A world leader in
the vaccine industry, Sanofi Pasteur offers the broadest range of vaccines
protecting against 20 infectious diseases. The company's heritage, to create
vaccines that protect life, dates back more than a century. Sanofi Pasteur is
the largest company entirely dedicated to vaccines. Every day, the company
invests more than EUR 1 million in research and development. For more
information, please visit: www.sanofipasteur.com or
www.sanofipasteur.us

1. Dengue vaccine efficacy trials in progress,
www.thelancet.com/infection, vol 9, November 2009

2. Jean Lang, Recent progress on Sanofi Pasteur's dengue vaccine
candidate. Journal of Clinical Virology 46, S2 (2009) 20-24

3. WHO Fact sheet No117, March 2009 Dengue and dengue haemorrhagic fever

4. Saville et al, Clinical development of a tetravalent dengue vaccine
for endemic areas, ICID Miami, March 2010; Lang et al, Toward a tetravalent
dengue vaccine in Brazil, Tropical Medicine meeting, Iguacu Falls, March 2010

5. PDVI Newsletter No 7, April 2010 accessible at
www.pdvi.org/PDVI_newsletter/newsletter.asp

Forward Looking Statements

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inherent in research and development, future clinical data and analysis,
including post marketing, decisions by regulatory authorities, such as the
FDA or the EMA, regarding whether and when to approve any drug, device or
biological application that may be filed for any such product candidates as
well as their decisions regarding labelling and other matters that could
affect the availability or commercial potential of such products candidates,
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commercially successful, the future approval and commercial success of
therapeutic alternatives, the Group's ability to benefit from external growth
opportunities as well as 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, 2009. Other than as required by applicable law, sanofi-aventis
does not undertake any obligation to update or revise any forward-looking
information or statements.

www.sanofipasteur.us

www.sanofipasteur.com

Contacts: Global Media Relations, Pascal Barollier, T. +33-(0)4-37-37-50-38, pascal.barollier at sanofipasteur.com; US Media Relations, Len Lavenda, T. +1-570-957-0717
len.lavenda at sanofipasteur.com