* Disappointing data raise questions about shot's potential
* Malaria infects some 219 million people a year worldwide
* RTS,S vaccine designed for use in Africa, among children
* GSK says full data on RTS,S will give clearer picture
By Kate Kelland and Gene Emery
LONDON/NEW YORK, March 20 The effectiveness of
an experimental malaria vaccine developed by GlaxoSmithKline
wanes over time, with the shot protecting only 16.8
percent of children over four years, according to trial data.
The disappointing results for RTS,S - the world's first
potential malaria vaccine - raise further questions about
whether it can make a difference in the fight against the
disease, a major cause of illness and death among children in
Results from a separate trial last year showed the vaccine
was only 30 percent effective in babies.
"The results are kind of disappointing because we'd all like
to see a malaria vaccine that has closer to 80 percent or 100
percent efficacy," said Christopher Plowe, a malaria researcher
at the University of Maryland School of Medicine in the United
States, who was not involved in the RTS,S trial.
Published in the New England Journal of Medicine on
Wednesday, the new data found that although RTS,S initially had
a protection rate as high as 53 percent, after an average of
eight months that effectiveness faded swiftly.
"It was a bit surprising to see the efficacy waned so
significantly over time. In the fourth year, the vaccine did not
show any protection," said Ally Olotu of the Kenya Medical
Research Institute (KEMRI) Wellcome Trust Research Programme in
Kenya, who led the follow-up study.
There is currently no vaccine that offers complete
protection against malaria.
The disease is caused by a parasite carried in the saliva of
mosquitoes and is endemic in more than 100 countries worldwide.
According to the World Health Organisation, malaria infected
around 219 million people in 2010, killing some 660,000 of them.
Control measures such as insecticide-treated bednets, indoor
spraying and anti-malaria drugs have helped cut malaria cases
and deaths significantly in recent years, but drug resistance is
growing and experts say an effective vaccine could be a vital
tool in eradicating the disease.
MOST ADVANCED CANDIDATE
GSK's RTS,S is the most advanced candidate malaria vaccine
in development and full data from final-stage trials involving
more than 15,000 children are expected by the end of next year.
A spokeswoman for GSK said since Wednesday's results were
from a small, mid-stage trial, they did not "provide definitive
answers about the duration of protection or how the vaccine
candidate works in different malaria transmission settings".
The British drugmaker is developing RTS,S for children in
Africa and has said it does not plan to make any significant
profit on the project if the vaccine gains marketing approval.
The study involved 447 children in Kilifi, Kenya, who had
been part of a mid-stage, or phase II, trial to assess the
safety and efficacy of RTS,S. Of the 447 children, 320 were able
to be followed up for four years.
Phillip Bejon, a researcher at the KEMRI-Wellcome Trust
programme who also worked on the study, said despite the falling
efficacy "there is still a clear benefit to the vaccine".
"Many of the children (in Africa) will experience multiple
episodes of clinical malaria infection, but overall we found
that 65 cases of malaria were averted over the four-year period
for every 100 children vaccinated," he said.
"We now need to look at whether offering a vaccine booster
can sustain efficacy for longer."
The researchers also found, however, that children exposed
to more malaria tended to see their protection against the
disease fade faster. Olotu said it was not clear why, but one
possible explanation might be that children normally get natural
immunity to malaria as they are exposed to it.
"But if you have a malaria vaccine that prevents exposure in
the first place, the children might be acquiring natural
immunity at a much slower rate compared to children who are not
getting the vaccine," Olotu said.