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* Study raises questions over deployment of vaccine
* Mosquirix not perfect but still has life-saving potential
* Could provide springboard for second-generation vaccines
By Kate Kelland, Health and Science Correspondent
LONDON, June 29 (Reuters) - The world's first malariavaccine, developed by GlaxoSmithKline, provides someprotection after three doses but its effect dwindles to almostnothing after seven years, scientists said on Wednesday.
Publishing a long-term study of the vaccine - called RTS,Sor Mosquirix and designed for children in Africa where thedisease claims most of its victims - researchers said thedecline in its efficacy over time is fastest in children livingin areas with higher than average rates of malaria.
This raises questions about whether Mosquirix can play ameaningful role in fighting malaria, they said, and suggests afour-dose schedule would be needed if it were used.
"The results suggest that the implementation of RTS,S willneed to be considered carefully and in a way that takes intoaccount different levels of malaria exposure," said Mike Turner,head of infections at the Wellcome Trust global health charitywhich helped fund the research.
He added that while the vaccine "isn't perfect", it stillhas the potential to save lives "and will provide an importantspringboard for improved second-generation vaccines".
Malaria, a mosquito-borne parasitic disease, kills around400,000 people a year, the vast majority of them children andbabies 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 dashedwhen trial data in 2011 and 2012 showed that Mosquirix reducedmalaria 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 thefirst ever malaria vaccine to win regulatory approval, when theEuropean Medicines Agency gave it a green light. The WHO,meanwhile, has said that Mosquirix is promising in its potentialto reduce cases of malaria, but should be deployed only on apilot basis before any wide-scale use.
For this latest study, published in the New England Journalof Medicine, researchers at the KEMRI-Wellcome Trust researchprogramme in Kilifi, Kenya, followed 447 children who hadreceived three doses of either Mosquirix or a control vaccinewhen they were 5 to 17 months old. After seven years, there were312 children still involved in the study.
The results showed that during the first year, the risk ofgetting malaria in the vaccinated children was 35.9 percent lessthan in the control group, but after seven years this differencefell to 4.4 percent.
After five years, in children exposed to higher than averagerates of malaria, there were more cases (1,002) in thevaccinated 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 vaccinatedchildren developing their natural immunity against malaria moreslowly than unvaccinated children.
GSK, which has been working on Mosquirix for 30 years, haspromised it will make no profit from it, pricing it at the costof manufacture plus a 5 percent margin which it will reinvest inresearch on malaria and other neglected tropical diseases. Theshot also contains an adjuvant, or booster, made by the U.S.biotech company Agenus. (Reporting by Kate Kelland)
