Rev. Inst. Med. Trop. Sao Paulo
54(Suppl. 18):S15-S17, October, 2012
Presented at the I International Symposium on Dengue of the School of Medicine University of São Paulo on October 6, 2011.
(1) Associate Vice-President, R&D Dengue Vaccine Program Head, Sanofi Pasteur, Lyon, France
DEVELOPMENT OF SANOFI PASTEUR TETRAVALENT DENGUE VACCINE
With almost 50% of the world population at risk and an estimated
annual burden that includes 230M infections, 2M severe cases and
25000 deaths, dengue is a major public health concern. Brazil is a
priority country for dengue vaccination as it accounts for 70% of all
reported cases in Americas (1998-2009) and > 1 million clinical cases
reported in 2010. After decades of research by different groups around
the world, dengue vaccine development reached a major milestone in
2010 with the initiation of the first phase III clinical trial to investigate
a candidate vaccine. This vaccine is the Sanofi Pasteur CYD tetravalent
dengue vaccine (TDV) which is now being evaluated for protective
efficacy in large scale trials in Latin America and south-east Asia as part
of an extensive clinical development program in both regions. The CYD
TDV candidate comprises four recombinant, live, attenuated vaccines
(CYD-1–4) based on a yellow fever vaccine 17D (YF17D) backbone,
each expressing the pre-membrane and envelope genes of one of the four
dengue virus serotypes. The vaccine is genetically and phenotypically
stable, non-hepatotropic, less neurovirulent than YF17D, and does not
infect mosquitoes by the oral route. In vitro and in vivo preclinical
studies showed that CYD TDV induces controlled stimulation of human
dendritic cells, and significant immune responses in monkeys that cross-
react against a panel of approximately 20 different circulating strains per
serotype. Scale up and industrialization are being conducted in parallel
with preclinical and clinical development to fulfill the needs of phase II/
III trials, and to anticipate and facilitate supply and access to vaccine in
the countries where the dengue disease burden makes it an urgent public
health priority. As of September 2011, the vaccine has been administered
to more than 11,000 children and adults in completed or ongoing studies
and no safety concerns have arisen. Given with a three-dose regimen,
vaccination induces balanced immune responses against all four serotypes
in the large majority of vaccinees. Preexisting flavivirus immunity favors
quicker and higher immune responses to CYD TDV, without adversely
effecting clinical safety or increasing vaccine viremia. The observed level
and nature of the cellular immune responses in humans are consistent with
the good safety and immunogenicity profile of the vaccine. Preliminary
results of an ongoing efficacy and large scale safety study in Thai children
are expected by the end of 2012 and we envisage the availability of this
vaccine for high disease burden countries in the next three to five years.
The worldwide expansion of dengue fever is major public health
concern. Dengue has become the most common tropical disease in
Latin America and Asia Pacific, and worldwide dengue is second only
to malaria. Almost 50% of the world population lives in areas at risk
for dengue. Each year more than 230 million people are infected; two
million patients develop severe disease, especially children (90%), and
25,000 patients die1-3.
Dengue is spreading in different areas and the burden of disease has
increased substantially in recent decades. Brazil accounts for the majority
of cases registered in the Americas, with more than one million dengue
cases, almost 100,000 hospitalizations and more than 600 deaths in 20104.
There is no specific treatment against dengue and vector control
measures have limited impact, particularly with the development of
insecticide resistance among the mosquito population. The availability
of a dengue vaccine would represent a major advance in the control of
In the last 40 years, different approaches have been used by academic
and industrial laboratories to develop dengue vaccine candidates.
These include live attenuated virus (LAV), recombinant virus vectors
expressing dengue envelope (E) antigens, purified inactivated virus
(PIV), recombinant subunit vaccine, virus-like particles (VPLs), and
Live vaccines have been shown to produce robust, long-lasting and
broad humoral and cellular immune response, but are associated with
a higher rate of adverse events, and cannot be used in some at-risk
groups, such as in immunocompromised people. Inactivated vaccines
have reduced potential for reactogenicity, but tend to have a diminished
ability to induce broad and durable immune responses6.
Several dengue vaccines are at various stages of evaluation. The
early enthusiasm about the tetravalent LAV dengue vaccines, developed
with classic empirical techniques of attenuation by serial cell passages,
was impacted by the difficulty of achieving an appropriate balance
between immunogenicity and reactogenicity. The vaccine strains
were genetically and phenotypically unstable, and caused dengue-
like syndromes (fever, leucopenia, and rash) in high proportion of
participants in early clinical trials6. A second generation of dengue
vaccines was developed to surmount these problems. In the early 2000´s,
Acambis discovery scientists (now Sanofi Pasteur) designed a second
generation of flavivirus vaccines, using an innovative recombinant
DNA technology to produce four live, attenuated vaccine viruses
based on yellow fever 17D vaccine strain, one per dengue serotype.
LANG, J. - Development of Sanofi Pasteur tetravalent dengue vaccine. Rev. Inst. Med. Trop. Sao Paulo, 54(Suppl. 18), S15-S17, 2012.
Each recombinant virus (CYD1, CYD2, CYD3 and CYD4) was
constructed by removing the genes encoding the premembrane (prM)
and envelope (E) proteins from the yellow fever 17D virus and inserting
the corresponding genes from a dengue virus8. Using this technology,
Sanofi Pasteur has preclinically, clinically and industrially developed
a tetravalent dengue vaccine, combining the four CYD vaccine viruses
into a single vaccine. This dengue candidate vaccine is the first to reach
the milestone of clinical phase III studies8.
There are many hurdles to the development of a successful dengue
- The lack of an animal model that reproduces human disease. Non-
human primates can be infected but do not develop disease.
- Four dengue virus serotypes can cause serious diseases, and the
immunity conferred by an infection is serotype-specific, with only a
short period of cross-protection against infection by other serotypes.
- There is a theoretical risk of immunopotentiation or sensitization
after sequential monovalent infections, which has been proposed
to be caused, in part, by antibody dependent enhancement (ADE),
associated with heterologous non-neutralizing antibodies and/or the
waning of homologous neutralizing antibody titers.
- Neutralizing antibodies against the dengue envelop proteins are
considered to be essential for protection, but there is no known
correlate of protection, and candidate vaccines must be studied
for efficacy in large numbers of individuals, in accordance with
guidelines for the clinical evaluation, production and quality control
recommended by WHO.
The ideal dengue vaccine would have a good safety profile, the
ability to elicit broad and durable immune responses against all four
serotypes, and be suitable for use in children and adults. Live vaccines
usually confers long lasting protection, but the development of multivalent
live vaccines is complicated by the potential for interference between
serotypes which can result in the immunodominance of one or two
serotypes, and can necessitate several doses to achieve an antibody
response to all serotypes6,7.
Dengue affects people in all age groups. Virus circulation differs
between regions, even within the same country. Vaccination schedules,
including for other flaviviral diseases (yellow fever and Japanese
encephalitis), differ between countries. How to fit a new vaccine into
existing national immunization programs therefore requires careful
consideration. It is therefore necessary to study the potential of
interference of a dengue vaccine candidate when co-administered with
Pragmatic issues, such as storage and the logistics of distributing a
high number of doses while maintaining the cold-chain, and strategies to
reach compliance with the recommended schedule and achieve suitable
vaccine coverage rates require discussion with health authorities before
implementation of a dengue vaccine9.
The effective use of the vaccine in the field will require partnerships
and collaboration among public and private sectors of endemic countries
to define where and how to introduce the vaccine. The ultimate goal will
be to design effective vaccination programs to alleviate the growing
global disease burden and pharmacoeconomic disruptive impact of
Other challenges relate to the industrialization of vaccine production
for the four vaccine viruses, and the manufacturing process scale-up
necessary to supply large-scale Phase III trials to demonstrate the
protective efficacy, and to prepare for the subsequent launch in case of
licensure7-10. Sanofi Pasteur has constructed new facilities to scale up
the production, and facilitate supply and access to vaccine as soon as
Extensive pre-clinical research has demonstrated the genotypic and
phenotypic stability of the CYD vaccine strains and has shown that
reversion to virulence or the recombination with other flaviviruses is
highly unlikely. The risk of inadvertent environmental dissemination of
the CYD viruses via mosquitoes has also been shown to be minimal7,8,11-13.
Other issue related to a candidate vaccine is its capability to protect
against different genotypes of dengue, and we had shown that our
candidate vaccine induces cross-reactive responses against a panel of
about 20 different circulating strains per serotype8. “Cross-neutralizing
antibody responses against circulating DENV field isolates after human
vaccination with a tetravalent dengue vaccine14,15.
Phase I and II clinical trials with a 3-dose vaccination regimen over
12 months demonstrate that this candidate vaccine elicits neutralizing
antibodies against all four serotypes in both children and adults with a
good safety profile13,16,17.
The global clinical development program includes 45,000 participants
from 15 countries8. To date (February 2012), more than 23,000
individuals, aged two to 45 years have received at least one dose of CYD
dengue vaccine in completed or ongoing studies8. Vaccine safety is being
monitored by an Independent Data Monitoring Committee (IDMC), an
independent group of international experts, and so far no safety signals
have been identified. A pooled analysis of safety data available in June
2011, including 1,728 subjects from 5 Phase I studies (USA, Mexico,
Philippines) and eight phase II studies (six completed) also revealed no
safety concerns. Reports of solicited reactions and unsolicited adverse
events were similar to those of the control vaccines, and tend to decrease
in frequency after second and third vaccinations compared to first
vaccination. Vaccine viremia is undetectable in the large majority of
vaccinees, and when detected the level of viremia has remained low. There
have been no reports of dengue-like syndrome or serious adverse events
related to this vaccine, in contrast to live attenuated vaccines developed
by conventional attenuation techniques. Furthermore, the safety profile
has been shown to be comparable in individuals with or without prior
exposure to dengue of other flavivirus, via infection or vaccination (YF,
JE)7,8,14. While all available data show that the vaccine’s safety profile is
good, with no safety signals detected after the vaccination of more than
23,000 vaccinees so far, the potential risk of very rare adverse events
cannot be determined until the licensure and introduction of the vaccine.
Other questions that cannot be definitively answered until after vaccine
introduction concern herd protection, efficacy of alternative schedules
(intention to treat), and the duration of protection in endemic and non-
The first phase III study was initiated in 2010 in Australia to evaluate
lot-to-lot consistency. The first efficacy study, including 4,000 children
(4-11 years) is ongoing in a highly endemic area of Thailand, and the
results are expected for the end of 2012. Positive results from this
LANG, J. - Development of Sanofi Pasteur tetravalent dengue vaccine. Rev. Inst. Med. Trop. Sao Paulo, 54(Suppl. 18), S15-S17, 2012.
study, conducted in an area where the force of infection is high would
represent the first time clinical efficacy has been demonstrated with a
dengue vaccine, and would allow us to consider initial submission to the
regulatory authorities in some countries8.
To expand the efficacy database in different countries, two other phase
III efficacy studies are ongoing in Asia (Thailand, Indonesia, Malaysia,
Viet Nan, Philippines), with planned inclusion of about 10,000 children
(2-14 years) and Latin America (Colombia, Mexico, Honduras, Porto
Rico and Brazil) where the number of enrolled children aged 9-16 years
is expected to be 20,000.
In conclusion, the CYD tetravalent dengue vaccine candidate
has demonstrated its capacity to induce broad and balanced immune
responses against the four dengue serotypes in children and adults from
endemic and non-endemic areas with a 3 dose vaccination regimen at
0, 6, 12 months. All available data show the vaccine’s safety profile to
be good, with no safety signals detected after the vaccination of more
than 23,000 vaccinees so far. The outcome of the first dengue vaccine
efficacy trial will be known by the end of 2012 and if positive will pave
the way for initial licensure and the immunization of populations against
this burdensome disease.
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