The vaccine maker Sanofi Pasteur says tests of its H1N1 flu vaccine suggest that children under ten may need two doses to be fully protected.

The U.S. Centers for Disease Control and Prevention says Wednesday's news is not surprising. This age group needs two doses of regular seasonal vaccine for full immunity to develop.

Federal officials have been hoping that one shot or squirt of nasal spray would do, so they can stretch the available supply of a vaccine much in demand.

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