About 150,000 doses of H1N1 vaccine for children were recalled in the US state of Texas because of concerns that they are not strong enough, state health authorities said Tuesday.

Nationwide, nearly a million doses of the H1N1 flu vaccine are being recalled, health officials said Tuesday.

Texas received about 150,000 of the 800,000 recalled doses, which were given to children six months to 3-years-old, they said.

Those questionable doses went to about 1,650 providers across Texas and most were shipped in November, said Carrie Williams, a spokeswoman for the Texas Department of State Health Services. She said officials are contacting providers by e-mail Tuesday afternoon asking them to set the vaccines aside.

"We've been working to pinpoint who received what and provide notifications of what to do," Williams said.

The vaccines, made by Sanofi Pasteur, the vaccines division of France-based Sanofi-Aventis Group, were distributed across the country last month and most have already been used, according to the Centers for Disease Control and Prevention (CDC).

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, authorities said.

The issue is the strength of potence. Officials with the Food and Drug Administration, the CDC and the company all said they believe the recalled doses is still strong enough to protect children against the virus.

H1N1 flu vaccine has been available since October and since then, manufacturers have sent about 95 million doses for distribution in the United States.

(Xinhua News Agency December 16, 2009)