Sanofi Pasteur Initiates Phase III Study of Investigational Clostridium Difficile Vaccine

Lyon, France - August 5, 2013 - Sanofi Pasteur, the vaccines division of Sanofi
(EURONEXT: SAN and NYSE: SNY), announced today the initiation of its Phase III
clinical program called Cdiffense to evaluate the safety, immunogenicity and
efficacy of an investigational vaccine for the prevention of primary
symptomatic Clostridium difficile infection (CDI). Clostridium difficile
(C. diff) is a potentially life-threatening, spore-forming bacterium that
causes intestinal disease. The risk of C. diff increases with age, antibiotic
treatment and time spent in hospitals or nursing homes, where multiple cases
can lead to outbreaks. The investigational vaccine is designed to help protect
at-risk individuals from C. diff, which is emerging as a leading cause of
life-threatening, healthcare-associated infections (HAIs) worldwide.(1)

C. diff toxins cause gastrointestinal disease that can lead to death in
approximately eight to 15 percent of infected people.(2) Since 20 to 30 percent
of patients experience recurrences of CDI, re-hospitalizations and longer
hospital stays remain common.(3) Combined data from the United States (U.S.) and
European Union (EU) indicate that healthcare systems spend more than $7 billion
annually on CDI acute care.(4),(5) Globally, there has been an increase in the
incidence and severity of CDI reported in North American,(6) European and Asian
countries, possibly due to the emergence of hyper-virulent strains.(7) The
investigational C. diff vaccine is designed to produce an immune response that
targets the toxins generated by C. diff bacteria, which can cause inflammation
of the gut and lead to diarrhea. It ultimately may help prevent a future
infection from occurring.

"With the emergence of difficult-to-manage strains of C. diff, CDI has become
more frequent, more severe and more difficult to treat in recent years, raising
concerns about how to control it and prevent transmission", explained John
Shiver PhD, Senior Vice President for Research & Development at Sanofi Pasteur.
"Vaccination could be an efficacious, cost-effective and important
public-health measure to protect individuals from C. diff."

The Cdiffense Phase III clinical program has just started recruiting volunteers
for a randomized, observer-blind, placebo-controlled, multi-center,
multi-national trial that will include up to 15,000 adults at 200 sites across
17 countries. Volunteers for the study should be age 50 or older and planning
an upcoming hospitalization or have had at least two hospital stays and have
received systemic antibiotics in the past year. For more information on the
Cdiffense trial, please visit

About C. diff
Clostridium difficile (C. diff) is a potentially life-threatening, spore-forming
bacterium that causes intestinal disease. The risk of contracting CDI increases
with age, antibiotic treatment and time spent in hospitals or nursing homes,
where multiple cases can lead to outbreaks.1 A main source of C. diff is
infected patients who release spores into the environment that can then infect
other people. When antibiotics disrupt the gut?s normal flora and a person has
ingested C. diff spores, the C. diff bacteria multiply and release potent
toxins that can damage a person's intestinal lining and cause C. diff

About Sanofi
Sanofi, an integrated global healthcare leader, discovers, develops and
distributes therapeutic solutions focused on patients' needs. Sanofi has core
strengths in the field of healthcare with seven growth platforms: diabetes
solutions, human vaccines, innovative drugs, consumer healthcare, emerging
markets, animal health and the new Genzyme. Sanofi is listed in Paris
(EURONEXT: SAN) and in New York (NYSE: SNY).

Sanofi Pasteur, the vaccines division of Sanofi, provides more than 1 billion
doses of vaccine each year, 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: or

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in Sanofi's annual report on Form 20-F for the year ended December 31, 2012.
Other than as required by applicable law, Sanofi does not undertake any
obligation to update or revise any forward-looking information or statements.


Global Media Relations          U.S. Media Relations
Alain Bernal                    Susan Watkins
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(1) Centers for Disease Control and Prevention. Frequently Asked Questions about
Clostridium difficile for Healthcare Providers. Centers for Disease Control and
Prevention. Last
Updated March 6, 2013. Accessed June 26, 2013.
(2) Mitchell BG and Gardner A. (2012) Mortality and Clostridium difficile
infection: a review. Aric journal.
(3) Garey KW, et al. (2008). Meta-analysis to assess risk factors for recurrent
Clostridium difficile infection. Journal Hospital Infection, 70, p. 298-304.
(4) Dubberke ER and Olsen MA. Burden of Clostridium Difficile on the Healthcare
System. Clinical Infectious Diseases 55, no. suppl 2 (2012): S88-S92.
(5) European CDC, Clostridium Difficile basic facts. Accessed June 26, 2013.
(6) Centers for Disease Control and Prevention. Making Health Care Safer:
Stopping C. difficile Infections. Centers for Disease Control and Prevention. Last Updated August 21, 2012.
Accessed June 26, 2013.
(7) Jones AM, Kuijper EJ and Wilcox MH. Clostridium difficile: A European
perspective. Journal of Infection 2013; 66(2): 115-128. Accessed
June 26, 2013.
(8) Delmee M and Warny M. (1995). Clostridium difficile colitis: recent
therapeutical and immunological considerations. Acta Gastroenterol Belg, 58
(3-4), p. 313-317.

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