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* Currently no vaccine for expanding mosquito-borne disease
* 56 pct efficacy hides mixed picture by virus strain
* Vaccine poor at protecting young children, most at risk
* Likely to serve endemic countries more than travellers
By Natalie Huet
PARIS, July 11 The first vaccine against dengue
fever, from France's Sanofi, provided moderate
protection in a large clinical study, but questions remain as to
how well it can help fight the world's fastest-growing tropical
The late-stage trial involved 10,275 healthy children aged
2-14 across five countries in Asia, a region that accounts for
over two-thirds of the mosquito-borne disease's global burden.
Sanofi had already disclosed in April that its vaccine
reduced the incidence of dengue fever by 56 percent in the Asian
study, without giving details. The full findings were published
online on Friday in The Lancet medical journal.
The study found the vaccine was safe and reduced the most
serious cases of haemorrhagic fever by nearly 90 percent. But it
offered poor protection to young children - who are most at risk
from dengue - and proved notably inefficient in tackling one of
the viral disease's four strains.
The results suggest the new vaccine acts best as an immune
booster for patients with some previous exposure, and therefore
may be most useful in tropical regions where dengue is common,
rather than as a vaccination for travellers.
Since there is no vaccine now, that could still make it an
important weapon in the fight against dengue.
"In view of the high disease burden in endemic countries...
this vaccine candidate, despite moderate overall efficacy, could
have a substantial effect on public health," the scientists
behind the study wrote.
The study was led by Maria Rosario Capeding from the
Research Institute for Tropical Medicine in the Philippines, and
funded by Sanofi.
Nearly half the world's population is at risk of contracting
dengue fever - also known as "breakbone fever" because of the
severe pain it can cause. The disease infects some 100 million
people each year, according to the World Health Organization,
and some experts put the number at triple that level.
Most patients survive dengue but it kills an estimated
20,000 people each year, many of them children, and causes one
hospitalisation every minute around the globe.
Sanofi has invested over 1.3 billion euros ($1.77 billion)
in the past 20 years in developing the vaccine, which is several
years ahead of potential competitors, and has built a dedicated
factory near Lyon in southern France with capacity to produce
100 million doses a year.
The company plans to establish a separate division within
its vaccines business to manage the rollout of the new product.
Some analysts believe the three-dose vaccine could sell 1
billion euros a year, significantly boosting Sanofi's vaccines
business, which generated sales of 3.7 billion euros in 2013.
But there are many uncertainties about commercial prospects
- including whether three shots of what is likely to be a pricey
vaccine are really needed, since one of the findings from the
latest study was that efficacy after at least one dose was
almost as high as after three doses.
Sanofi is still testing its vaccine in 20,000 children in
Latin America and Guillaume Leroy, head of its dengue vaccine
programme, said it would await the results of that final study -
due by the year-end - before seeking regulatory approval in
endemic countries next year.
Coming up with a vaccine that can protect against the
disease has puzzled scientists for over 70 years, since the
movement of troops during World War II helped dengue spread
across the Pacific and become a worldwide pandemic.
In the Asian study, the vaccine provided only 35 percent
protection against serotype 2.
A 2012 study in Thailand had already shown that the vaccine
was unable to tame serotype 2, which happened to be most
prevalent at the time of the study. This time, serotype 2 was
less prevalent among patients, drawing the vaccine's overall
efficacy rate higher.
Annelies Wilder-Smith of Singapore's Nanyang Technological
University, who wrote a commentary accompanying the Lancet
study, said its failure in serotype 2 was "an enigma".
Questions remain as to what the threshold of dengue
incidence might be for countries to decide that it is worth
launching costly vaccination programmes, she noted.
Difficulties in developing a dengue vaccine echo similar
problems that GlaxoSmithKline has had in developing the
first vaccine for malaria, which also did not perform as
strongly in clinical trials as initially hoped.
($1 = 0.7331 Euros)
(Additional reporting by Ben Hirschler in London, editing by