Siegel agreed that the small drop in potency is not enough to require another vaccination. "The children that received this vaccine are very likely to have a significant amount of immunity, because the immune response as tested in studies was profound," he said.
The CDC points out that for children aged 6 months and older, vaccine in multi-dose vials is available. Vaccine in multi-dose vials has not had this drop in potency and "meets all standards of safety, purity and potency."
Like all multi-dose vials of vaccines, these vials contain thimerosal to prevent contamination after the vial is opened. The standard dose from these vials is the same as for the pre-filled syringes.
In addition, for children aged 2 and older, the H1N1 vaccine is also available as a nasal spray called Flumist.
Since early October, about 95 million doses of swine flu vaccine have been distributed in the United States.
For more information on the H1N1 flu, visit Flu.gov.
SOURCES: Marc Siegel, M.D., associate professor, medicine, New York University, New York City; Dec. 15, 2009, statement, U.S. Centers for Disease Control and Prevention
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