The recalled shots were made by Sanofi Pasteur, the vaccines division of France-based Sanofi-Aventis Group. The vaccine tested fine when it was shipped out earlier this fall. But last week, testing of one lot showed that the potency had fallen about 12% below the government standard, Lavenda said.
The company found three other lots with diminished strength. It notified government health officials and did a voluntary recall, asking doctors to return any unused doses. The vaccine has been in high demand and the company doesn't expect to see much come back, Lavenda added.
Officials with the Food and Drug Administration, the CDC and the company all said they believe the strength of the recalled doses is still high enough to protect children against the virus. No potency problem has been detected in the same vaccine packaged in other types of syringes or vials, Lavenda said.
Experts have a theory that the problem is specific to the children's pre-filled syringes. For some reason, the antigen — the key vaccine ingredient — may be sticking to the walls of those syringes, said Dr. Jesse Goodman, the FDA's deputy commissioner for science and public health.
Another manufacturer, Novartis, in February recalled five lots of seasonal flu vaccine packed in pre-filled syringes under similar circumstances.
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.
Swine flu was first identified in April. During the first seven months of the pandemic, it has sickened about 50 million Americans and killed about 10,000, according to CDC estimates.
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