GENEVA/LONDON (Reuters) - The world's first malaria vaccine is promising but should be used on a pilot basis before any wide-scale use, given its limited efficacy, World Health Organization experts said on Friday.

The Mosquirix shot, made by GlaxoSmithKline, could potentially help stop millions of cases of malaria in babies and young children in Africa at risk of the deadly mosquito-borne disease. However, it is less effective than vaccines against many other diseases.

Jon Abramson, chairman of the WHO Strategic Advisory Group of Experts, or SAGE, said experts recommended there should be three to five demonstration projects in children aged five to 17 months before considering any wider scale-up.

These projects would likely take three to five years to run and could involve around 1 million children, he added. SAGE did not recommend the use of Mosquirix, also known as RTS,S, in young babies.

Committee experts were particularly concerned that four doses of the vaccine should be administered to ensure optimal efficacy, even though getting children back for multiple repeat shots could be challenging.

“If we can’t get four doses of this vaccine into the children, we’re not going to be using it,” Abramson told reporters.

“What we are recommending is that before we have widespread use of this vaccine - and we wouldn’t necessarily use it in a very low incidence area, but in all medium and high areas - that we know that we can get that fourth dose in.”

Hopes that GSK's vaccine could wipe out malaria were dampened when trial data in 2011 and 2012 showed it reduced malaria episodes in babies aged six to 12 weeks by only 27 percent, and by about 46 percent in children aged five to 17 months. Part of that could be down to genetics.

GSK has said it will not make any profit from the vaccine, since it will be priced at the cost of manufacture plus a 5 percent margin, which will be reinvested in research on malaria and other neglected tropical diseases.

(Reporting by Ben Hirschler; Editing by David Holmes)