Publishing a long-term study of the vaccine - called RTS,S or
Mosquirix and designed for children in Africa where the disease
claims most of its victims - researchers said the decline in its
efficacy over time is fastest in children living in areas with
higher than average rates of malaria.
This raises questions about whether Mosquirix can play a meaningful
role in fighting malaria, they said, and suggests a four-dose
schedule would be needed if it were used.
"The results suggest that the implementation of RTS,S will need to
be considered carefully and in a way that takes into account
different levels of malaria exposure," said Mike Turner, head of
infections at the Wellcome Trust global health charity which helped
fund the research.
He added that while the vaccine "isn't perfect", it still has the
potential to save lives "and will provide an important springboard
for improved second-generation vaccines".
Malaria, a mosquito-borne parasitic disease, kills around 400,000
people a year, the vast majority of them children and babies in
sub-Saharan Africa. World Health Organization (WHO) data show there
are around 200 million malaria cases a year.
Hopes that GSK's shot could wipe out malaria were dashed when trial
data in 2011 and 2012 showed that Mosquirix reduced malaria episodes
in babies aged six to 12 weeks by 27 percent, and by about 46
percent in children aged five to 17 months.
Despite its limited efficacy, Mosquirix last year became the first
ever malaria vaccine to win regulatory approval, when the European
Medicines Agency gave it a green light. The WHO, meanwhile, has said
that Mosquirix is promising in its potential to reduce cases of
malaria, but should be deployed only on a pilot basis before any
For this latest study, published in the New England Journal of
Medicine, researchers at the KEMRI-Wellcome Trust research program
in Kilifi, Kenya, followed 447 children who had received three doses
of either Mosquirix or a control vaccine when they were 5 to 17
months old. After seven years, there were 312 children still
involved in the study.
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The results showed that during the first year, the risk of getting
malaria in the vaccinated children was 35.9 percent less than in the
control group, but after seven years this difference fell to 4.4
After five years, in children exposed to higher than average rates
of malaria, there were more cases (1,002) in the vaccinated group
compared with the control group (992).
Philip Bejon, director of the KEMRI programme, said this "rebound"
effect is thought to be caused by the vaccinated children developing
their natural immunity against malaria more slowly than unvaccinated
GSK, which has been working on Mosquirix for 30 years, has promised
it will make no profit from it, pricing it at the cost of
manufacture plus a 5 percent margin which it will reinvest in
research on malaria and other neglected tropical diseases. The shot
also contains an adjuvant, or booster, made by the U.S. biotech
(Reporting by Kate Kelland)
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