Hundreds of thousands of swine flu shots for children manufactured by French drug company Sanofi Pasteur have been recalled because tests indicate the vaccine doses lost some strength, government health officials said Tuesday.

The recall is for about 800,000 pre-filled syringes intended for young children, ages 6 months to nearly 3 years.

The shots were distributed across the country last month and most have already been used, according to the federal government's Centers for Disease Control and Prevention. Doctors were notified of the voluntary recall on Tuesday.

Slideshow: How to Avoid H1N1 This Holiday Season

Related: As Interest in H1N1 Vaccine Wanes, a Surplus Is Feared

Dr. Anne Schuchat, a CDC flu expert, stressed that parents don't need to do anything or to worry. The vaccine is still safe, she said. The issue is the vaccine's strength.

"No action (is) necessary by a parent of a child who received this vaccine," said Tom Skinner, a spokesman for the CDC. "(The) only thing they need to do is make sure their child gets two doses if they're in the 6 month - 35 month age group, which is the group impacted by the recall."

Tests done before the shots were shipped showed that the vaccines were strong enough. But tests done weeks later indicated the strength had fallen slightly below required levels. Why the potency dropped isn't clear.

Children in that age group are supposed to get two doses, spaced about a month apart. Health officials don't think children need to get vaccinated again, even if they got two doses from the same lots, said Schuchat.

Swine flu vaccine has been available since early October, and since then manufacturers have released about 95 million doses for distribution in the United States.

The recalled shots were made by Sanofi Pasteur, the vaccines division of France-based Sanofi-Aventis Group. The company reported the potency findings to the government officials and did a voluntary recall.

A Sanofi Pasteur representative could not immediately be reached for comment Tuesday. Sanofi Pasteur bills itself as the No. 1 manufacturer of flu vaccines in the world. It makes flu vaccine at sites in France and in Pennsylvania.

The Associated Press contributed to this article.

———

On the Net: CDC: http://www.cdc.gov/H1N1FLU/