Data from tests on adults show it is safe to start trying out the new H1N1 swine flu vaccine in children, U.S. officials said.

The National Institute of Allergy and Infectious Diseases said it would soon start two trials of Sanofi-Aventis' vaccine in children aged 6 months to 17 years old.

"The safety monitoring committee reviewed data from more than 500 healthy adult and elderly volunteers enrolled in three ... trials of candidate H1N1 vaccines that began Aug. 7, 2009," the NIAID, part of the National Institutes of Health, said in a statement.

"The committee found no safety concerns in those trials that would preclude trials from proceeding in children," it added.

One trial will enroll up to 650 children aged six months to 17 years in six U.S. cities who will get either a large or small dose of H1N1 vaccine in two shots three weeks apart.

A second trial will give children Sanofi's H1N1 vaccine before, after or at the same time as the seasonal flu vaccine.

Five companies are making both seasonal and H1N1 flu vaccines for the U.S. market — AstraZeneca's MedImmune unit, CSL, GlaxoSmithKline Plc, Novartis AG and Sanofi.

HHS says 45 million doses of the H1N1 vaccine will be on hand in mid-October, when mass vaccination is planned.

Because it takes months to make a vaccine and because the autumn flu season is looming, companies are making and testing the new vaccine at the same time as U.S. officials plan to start vaccinating.

The U.S. Food and Drug Administration is licensing the new influenza vaccine as if it were just a typical annual change in formulation done every year as the seasonal flu vaccine changes to match the drift, or slight mutations, in the circulating viruses.

Last month, the Advisory Committee on Immunization Practices recommended pregnant women, health care and emergency medical workers, people caring for infants under 6 months old, children and young adults from 6 months to 24 years old and people 25 to 64 years old with chronic medical conditions such as asthma and diabetes be vaccinated first — a total of 160 million people.