2nd dose of H1N1 vaccine elicits better response in youngest children

The National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, announced interim trial results that show that children 9 years old and younger have a significantly improved immune response when given a second 15-microgram dose of 2009 H1N1 influenza vaccine.

The clinical trial evaluated the immune response of children 6 months to 17 years of age who received two doses of either 15 or 30 micrograms of 2009 H1N1 influenza vaccine. One of the most important findings from this study is that among children 9 years old and younger, the second dose elicited a robust immune response after eight to 10 days, a significant improvement over the immune responses in this age group following only a single dose.

These findings announced Nov. 2 support the current recommendation of the Advisory Committee on Immunization Practices, which sets U.S. recommendations for all immunizations: To achieve an immune response likely to protect from illness, children 9 years of age and younger should receive two 15-microgram doses of 2009 H1N1 vaccine. The trial data also continue to support the recommendation that children 10 and older should receive only one 15-microgram dose of vaccine.

The interim results include data from all available samples from the 583 children enrolled into the trial, and build upon the preliminary results released Sept. 21 from a subset of volunteers.

In general, the immune responses in children receiving two 15-microgram doses and those receiving two 30-microgram doses of vaccine were similar, suggesting that receipt of two 15 microgram doses is adequate to elicit a strong immune response.

Analysis continues on the data from this trial, and additional findings will be provided as they become available.

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