* Sanofi shot works against 3 of 4 virus types in Thai study
* Drugmaker eyes dengue vaccine as potential blockbuster
* Full results of Phase IIb Thai trial due in September
* Vaccine may reach market in 2015
By Ben Hirschler and James Regan
LONDON/PARIS, July 25 The world's first vaccine
against dengue fever, being developed by French drugmaker Sanofi
SA, protected against three of the virus's four
strains in a keenly awaited clinical trial in Thailand.
Sanofi said on Wednesday the proof of efficacy was a key
milestone in the 70-year quest to develop a viable dengue shot,
adding the results also confirmed the safety profile of its
vaccine candidate, which could reach the market in 2015.
Other drug companies are also working on dengue vaccines but
Sanofi's product is several years ahead.
The mosquito-borne disease, also known as "breakbone fever",
is a threat to nearly 3 billion people and is caused by four
different types of virus, none of which confers immunity from
Sanofi's vaccine generated an antibody response for all four
dengue virus types, but evidence of protection was only
demonstrated against three of the four strains circulating in
Duane Gubler of the Duke-N.U.S. Graduate Medical School, who
has researched dengue for four decades, said the results looked
"great", despite the failure to defend against all strains.
"I am not at all concerned about the lack of protection
against all four serotypes. Based on what we know about the
immune response to dengue viruses, if the vaccine protects
against three serotypes, recipients will be protected against
severe disease," he said in an emailed exchange.
Sanofi said researchers were carrying out analyses to
understand the lack of protection for the fourth serotype.
"It's a surprise," company spokesman Pascal Barollier said.
"We need to get to the bottom of the data to find out why it is
reacting this way and wait for ongoing Phase III trials to see
if it is linked to some specific situation in Thailand."
The Phase IIb study involving 4,002 Thai children aged four
to 11 years was conducted during a dengue epidemic, which might
be an explanation for the unexpected outcome.
Deutsche Bank analyst Mark Clark said the lack of protection
against the fourth virus type meant a commercial launch was more
likely in 2015 than in 2014, as Sanofi awaits Phase III data
rather than filing early in some countries.
"More positively, given that protection against at least
three of the four viral types has been demonstrated, the data
supports the likelihood of launch for this huge unmet clinical
need," Clark wrote in a research note.
The company's vaccine unit Sanofi Pasteur has already
invested 350 million euros ($423 million) in a new French
factory to make the three-dose vaccine and believes its product
could generate more than 1 billion euros in yearly sales.
But uptake of the vaccine will depend on precisely how well
doctors believe it can protect populations at risk in
fast-expanding tropical cities from Rio to Manila, as well as
travelers to such areas.
Sanofi, which reports second-quarter results on Thursday,
gave no details on the level of protection in a brief statement.
The full data are now being reviewed by scientific experts and
public health officials, with detailed results to be published
later this year.
Barollier said the aim was to publish the study results in a
scientific journal in September and then present the research to
the American Society of Tropical Medicine and Hygiene in Atlanta
Large-scale late-stage Phase III clinical studies with
31,000 participants are under way with Sanofi's vaccine in 10
countries in Asia and Latin America.
Dengue fever, which can cause intense joint and muscle pain,
is spread by the bite of the Aedes aegypti mosquito. The insect
thrives in the mega-cities of the tropics, with the result that
nearly half the world's population are at risk of catching the
In the past 50 years there has been a 30-fold jump in dengue
cases. The World Health Organisation officially puts infections
at between 50 and 100 million a year, though many experts think
this assessment from the 1990s badly under-estimates the
Most patients survive but it is estimated to kill about
20,000 every year, many of them children less able to fight it