A WHO expert group says a single dose of swine flu vaccine is enough to immunize adults and children over 10 against the pandemic strain.
But the experts say medical regulators should have the final say on which vaccines can be administered as a single shot.
Europe's drug regulator recommends that the swine flu vaccines it has licensed be given in two doses, at least three weeks apart.
U.S. regulators recommend two doses for children under 10.
The WHO experts say more data on children aged between 6 months and 10 years are needed to determine whether one or two doses are enough.
WHO released the recommendations Friday after a three-day meeting of vaccine experts in Geneva.