The CDC says in a statement that the vaccines in pre-filled syringes are being recalled because tests indicate the doses in question have lost some of their original strength. The agency says the vaccines are safe.
The vaccine in question is for children 6 to 35 months of age, the CDC says. Made by Sanofi Pasteur, the syringes were distributed nationwide in November.
The agency says about 800,000 doses were distributed to providers.
Sanofi Pasteur, a division of France-based Sanofi-Aventis Group, notified the FDA and the CDC on Dec. 7 that one lot of pediatric syringes had dropped below a pre-specified active ingredient limit.
Sanofi Pasteur performs routine, ongoing stability testing of the H1N1 vaccine after it has been shipped to providers, measuring its potency. "As a result of this finding, Sanofi Pasteur tested additional lots and found that three other lots that had been distributed also had an antigen content that, while properly filled at the time of manufacturing, was later measured to be below pre-specified limits," the CDC says. "This means that doses from these four vaccine lots no longer meet the manufacturer's specifications for potency."
The CDC says the French company will send providers directions for returning unused vaccines from these four lots.
The CDC also says that infants and children who received vaccines from the affected lots do not need to be revaccinated because "potency is only slightly below 'specified' range" and that the vaccine "is still expected to be effective in stimulating a protective response despite this slight reduction in the concentration of antigen.
"There is no need to re-administer a dose to those who received vaccine from these lots," the CDC says. "However, as is recommended for all 2009 H1N1 vaccines, all children less than 10-years-old should get the recommended two doses of H1N1 vaccine approximately a month apart for the optimal immune response."
Children younger than 10 who have received only one dose should still receive a second one.
"Sanofi Pasteur is investigating what caused the problem," the CDC says. "The same vaccine packaged in other dosing forms, such as pre-filled syringes for older children [and] adults and multidose vials, continues to meet specifications."
It says this recall does not affect H1N1 vaccine produced by other companies.
The agency adds that vaccine is available in multidose vials for children 6 months of age and older. All multidose vials of vaccines contain the preservative thimerosal to prevent contamination, CDC says. For healthy children 2 and older, the nasal spray vaccine also is an option, the federal agency says, adding this form does not contain thimerosal.
"However," CDC says, "it is important that children receive both doses of H1N1 vaccine from the same type of vaccine" (both doses as shots or both doses as nasal spray vaccine).