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HEALTH: Dengue vaccine - still a long way off
LONDON, 11 September 2012 (IRIN) - Dengue fever is classed by the World
Health Organization (WHO) as a "major international public health
concern". WHO estimates that it infects 50-100 million people a year;
it is a leading cause of death among children in Asia and Latin
America, and it is now spreading outside its traditional heartlands to
Africa and the Middle East.
But dengue is difficult to deal with. There is no cure, only treatment
for the symptoms. And although there are effective vaccines against
related viruses, like yellow fever and Japanese encephalitis, no one
has yet succeeded in making a safe, effective vaccine against dengue.
Now a team of researchers working with the French drug company Sanofi
Pasteur has carried out a randomized trial of a possible vaccine,
involving more than 4,000 schoolchildren in northern Thailand, and have
produced some interesting results. Their vaccine was only partly
effective but the team's findings - reported in the British medical
journal, the Lancet
-7/abstract> - suggest that the development of a useful vaccine is
Derek Wallace of Sanofi-Pasteur, one of the authors of the report,
hailed their results as an important step. "Our study constitutes the
first ever demonstration that a safe and effective dengue vaccine is
possible," he says. "Further trials [of the vaccine] are currently
under way in a number of different countries, and we hope that the
positive results of this trial will be confirmed by these larger
The trial took place in Thailand's Muang District, based at Ratchaburi
Regional Hospital, and involved researchers from Bangkok's Mahidol
University. Children aged 4-11 from 35 local schools were enrolled in
the trials. Two-thirds of them were given three doses of the vaccine,
known as CYD-TDV (a recombinant, live, attenuated tetravalent vaccine,
based on yellow fever 17D vaccine strain, produced in Vero cells). The
control group received either rabies vaccine or a placebo.
The children were vaccinated three times, at six-monthly intervals, and
the researchers looked at the presence of dengue antibodies in their
blood, as well as checking all cases of fever, mild or serious, and
recording which were due to dengue.
'' This [study]
did not show the vaccine can prevent severe cases
The results were mixed. While the vaccine appears to be safe and well
tolerated, it had only a limited effect. It gave useful protection
against three strains of the disease, those known as DENV 1, 3 and 4.
But although the vaccinated children produced antibodies to DENV 2,
they still caught the disease just as often as the children in the
control group. And unfortunately DENV 2 is the most common strain of
dengue fever in northern Thailand.
Scott Halstead of the International Vaccine Institute in Seoul, points
out that even these results were made less useful by the fact that they
did not test the vaccine on teenagers, who are more likely to get the
severe form of the disease. He said: "Results from this vaccine trial
provide hard evidence of protection against DENV 1, 3 and 4 mild
disease but insufficient data to calculate vaccine efficacy rates for
severe disease. Future dengue vaccine trials should provide robust
evidence of efficacy against severe disease by selecting populations
weighted to assure inclusion of sufficient numbers of at risk children."
Bill Messer, clinical assistant professor at the Division of Infectious
Diseases in the University of North Carolina School of Medicine, is
blunter, pointing out that Sanofi Pasteur has been trying to refine the
vaccine for the past decade (it started presenting papers on it in
about 2001) but that the vaccine still cannot produce a "robust"
"This [study] is an encouraging first step, but far from where we need
to be. It did not show the vaccine can prevent severe cases. That is an
important endpoint [for a dengue vaccine]. You need to show recipient
populations protection against severe dengue in order to encourage
[vaccination]," he said.
While most dengue patients do not have symptoms or only mild pain and a
rash, up to 10 percent develop a lethal "severe" form of the disease
(previously known as dengue haemorrhagic fever). Only five children in
the study had severe dengue, too few to analyse, a limitation the
authors noted was being corrected in ongoing studies with 30,000 adults
and children in dengue-endemic countries.
Messer also said the number of people tested thus far in Thailand is
insufficient to prove the vaccine will not cause severe dengue. Health
experts have expressed concern that complications from a dengue vaccine
result in infection rather than confer protection.
Despite some positive results from the trials, it seems that a dengue
vaccine is still a long way off.
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[This report does not necessarily reflect the views of the United
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