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* Data show vaccine gives 46 pct protection for 15 months
* Late-stage trials ongoing, vaccine could be available 2015
* Could be promising public health measure - researchers
By Kate Kelland
LONDON, Jan 14 (Reuters) - An experimental malaria vaccine from GlaxoSmithKline provides African children with long-lasting protection, though its effectiveness declines slightly over time, according to trial data published on Friday.
Scientists conducting the mid-stage trial at the Kenya Medical Research Institute said results showing the shot offered 46 percent protection for 15 months meant it had "promise as a potential public health intervention against childhood malaria in malaria endemic countries".
Malaria is an infectious disease spread by mosquitoes that threatens up to half the world's population. Most of its victims are children under five in poor countries in sub-Saharan Africa.
The World Health Organisation's latest malaria report found progress against the disease has been made over the past decade, with deaths estimated to have dropped to 781,000 in 2009 from nearly a million in 2000.
Late-stage trials of the GSK vaccine, known as RTS,S or Mosquirix, in 16,000 children in seven countries across Africa are ongoing, with immunisations due to end next month.
If data show the vaccine was effective, it could be licensed and rolled out as soon as 2015.
The mid-stage study, conducted between March 2007 and October 2008, involved 894 children aged over five months in Kenya and Tanzania.
Initial findings published in 2008 showed the vaccine gave 53 percent protection against malaria for at least eight months, but researchers led by Ally Olotu at the institute in Kilifi, Kenya wanted to see if that protection would last longer.
Results published in The Lancet journal showed that after 15 months of follow-up, the efficacy of the vaccine had not waned much, with children who had been given the shot still 46 percent less likely to be infected with malaria than those who had not.
"Further studies are needed to establish vaccine efficacy in, for example, children with HIV infection or those who are malnourished," Olotu said in the study, adding further trials should also be done at sites with varying transmission intensities to confirm the results.
GSK chief executive Andrew Witty has said that if RTS,S proved effective in final-stage trials it would be sold at a price that those who need it most can afford. The company has said it was planning for a profit margin of 5 percent over the cost of making the vaccine, and that would be reinvested in new vaccines for malaria and other neglected diseases. (Editing by Ben Hirschler and Dan Lalor))